Mention the ability to use <Tab> in the search history, the ability
to restore the cursor position when reopening a file, the ability to
read output of a command, and the lack of file-managing commands in
the file browser.

The "./" is a shorthand for "current working directory".
It is better to specify it, because it differs from what
Pico does: reading always from the user's home directory
no matter where the editor was started.

Only use the "from" thing when an operating directory is in effect,
because /only/ then the indicated directory can be something other
than "./".

Also, make it so that there is no space before the colon.

And slightly change the existing one for normal users.

"Q" is a pretty standard key to exit from something, and "X" is fairly
mnemonic -- better than "E" at least.

Put all the movement keys together, in order of ascending stride.

Also, move the Undo/Redo keystrokes further up, so that, when the
user has a somewhat wider terminal than the usual 80 characters,
these keystrokes will be shown -- they are far more interesting
than the ^Y and ^V ones, for which PgUp and PgDn can be used.

But apparently none of these cases occur, because I can't trigger them.

This could happen when a tab or a double-width character straddles
the boundary between two softwrapped chunks.

If the number of columns in the edit window changes (which currently
only happens in two places: in regenerate_screen(), called when the
window is resized; and in main(), when line numbering mode is toggled),
the display will break if we're in softwrap mode and firstcolumn is
nonzero.  This is because the column width of softwrapped chunks has
changed, and firstcolumn is no longer the starting column of a chunk,
an assumption that all code using firstcolumn relies on.

To fix this problem, add a new function, ensure_firstcolumn_is_aligned(),
to adjust firstcolumn to the starting column of the chunk it's on, and
use it when the number of columns in the edit window changes.

(Note that this function uses the simplest possible fix, and could
probably be made more sophisticated.)

In do_replace(), replacing text may change firstcolumn if the next match
is offscreen, and replacing text after that will not change it back.  In
order to keep the viewport unchanged, we have to save and restore not
just edittop, but firstcolumn as well.

In do_int_spell_fix(), spell-checking text may change firstcolumn if
the next match is offscreen, and spell-checking text after that will
not change it back.  In order to keep the viewport unchanged, we have
to save and restore not just edittop, but firstcolumn as well.

In do_justify(), justifying text may change firstcolumn if the paragraph
ends offscreen, and unjustifying the text again will not change it back.
In order to keep the viewport unchanged, we have to save and restore not
just edittop, but firstcolumn as well.

Copying text involves first cutting it and then quickly pasting it back.
However, cutting the text may change firstcolumn if the mark is offscreen.
To keep the viewport unchanged, copy_text() has to save and restore not
just edittop, but firstcolumn as well.

Now that we can add text to the bottom right corner of the screen
without scrolling the full line onscreen, do_output() needs to refresh
the screen in that case, since it would put the cursor offscreen
otherwise.  Accomplish this by borrowing logic from do_right().

In do_up() when scroll_only is TRUE, if we're at the top of the screen
in softwrap mode, it's not enough to check that edittop is on fileage.
We also need to check that firstcolumn is zero.

In do_up() when scroll_only is FALSE, if we're at the top of the screen
in softwrap mode, current_y should be zero.  This is equivalent to how,
in do_down() when scroll_only is FALSE, current_y is (editwinrows - 1)
at the bottom of the screen in softwrap mode.  Since edittop can now
be partially scrolled off the screen even when it takes up the entire
screen, checking for edittop's being equal to openfile->current->next
there no longer applies.

The new function, update_softwrapped_line(), is called from inside
update_line() when softwrap mode is on, so that existing calls remain
unchanged.  It takes no index, instead displaying edittop from column
firstcolumn, and all other lines from column zero.

If current is on edittop, it's displayed using the edittop rules, but
this is not a problem: if current[current_x] is above edittop at column
firstcolumn, it's offscreen, and that should be handled before calling
update_line() anyway.

Together with the preceding bunch of changes,
this fixes https://savannah.gnu.org/bugs/?47667.

When counting rows in softwrap mode, reset_cursor() should compensate for
the number of softwrapped chunks that edittop takes up before firstcolumn.

Make current_is_above_screen() check for current[current_x] being above
edittop at column firstcolumn, and make current_is_below_screen() start
counting down from edittop at column firstcolumn instead of edittop at
column zero.  This means that both functions now account for softwrapped
chunks properly.

Actually enable scrolling edittop partially off the screen by making
edit_scroll() and adjust_viewport() use firstcolumn properly when
iterating through softwrapped chunks in softwrap mode, or lines in
non-softwrap mode.

In non-softwrap mode, firstcolumn should still always be zero, because
it's initially set to that, and because passing it through the iterators
will maintain it at that.

This fixes https://savannah.gnu.org/bugs/?49100

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

We want to be able to scroll the line at edittop partially off the
screen.  For this to be possible, the new variable firstcolumn stores
the starting column of the viewport -- the starting column in the line
that edittop points to.

Since firstcolumn is used by go_back_chunks() and go_forward_chunks(),
it can't be completely #ifdefed out when NANO_TINY is set, but outside
of softwrap mode it should always be zero.

Currently firstcolumn is initialized to zero, reset to zero when
toggling softwrap mode off, and reset to zero when switching buffers
while softwrap mode is off.  It's otherwise unused, but its uses are
forthcoming.

Since all lines can be partially scrolled off the screen now
(except for the top line of the edit window, which is forthcoming),
ensure_line_is_visible() is no longer needed.

Since all lines can be partially scrolled off the screen now
(except for edittop, which is forthcoming), the maxlines global
variable and its computation mechanism are no longer needed.

Use go_back_chunks() and go_forward_chunks() to move a screenful of
lines or chunks up or down, instead of using special computations in
the softwrap case.

Use go_back_chunks() and go_forward_chunks() in do_up() and do_down()
(instead of using a special and complicated computation in do_down())
so that they now properly move vertically to the previous/next chunk
in softwrap mode.  This also means that do_left() and do_right() will
now properly move vertically at actual line boundaries.

Use the new "unclever" functionality of Home and End to make do_left()
and do_right() move properly to the end of the previous chunk or to the
start of the next chunk in softwrap mode when crossing a line boundary.
(Furthermore, doing Up plus End, or Down plus Home, does all needed
screen updates, which simplifies the code.)

The do_left() and do_right() functions don't yet properly move vertically
at line boundaries, but that will be fixed once do_up() and do_down() are
updated for softwrap mode, which is forthcoming.

This fixes https://savannah.gnu.org/bugs/?49384.

Add the parameter be_clever to both functions.  When be_clever is FALSE,
smart home and dynamic home are disabled in do_home(), and dynamic end is
disabled in do_end(), so that these functions only move to the beginning
or end of the current line or chunk.

This simple home and end functionality is needed to improve do_left()
and do_right()'s horizontal behavior with softwrapped chunks, which is
forthcoming.

Make do_end() more useful in softwrap mode: let it move to the end of the
current chunk instead of the end of the line; only when already at the end
of a chunk, let it move to the end of the line.  This is "dynamic end".

Make do_home() more useful in softwrap mode: let it move to the beginning
of the current chunk instead of to the beginning of the whole line; only
when already at the beginning of a chunk, let it move to the beginning of
the line.  This is called "dynamic home'.

The above rules are ignored when --smarthome is in effect and the cursor
is somewhere in the leading whitespace of a line -- then the cursor is
moved to the first non-whitespace character of the line.

These improvements will eventually make do_home() and do_end() take
parameters.  Since the global function lists can hold only functions
without parameters, preemptively add do_home_void() and do_end_void(),
and make the global function lists use them.

Use go_back_chunks() and go_forward_chunks() to move from the row
current_y is on to the row mouse_row is on.  Now softwrap mode and
non-softwrap mode will behave the same way when we can scroll edittop
partially off the screen, which is forthcoming.  Accordingly, remove
the call to ensure_line_is_visible(), as it no longer applies.

The old code did work, but it behaved differently between softwrap mode
(which counted down from edittop) and non-softwrap mode (which counted
up or down from current_y to take less time, and used a double loop to
keep current from going to NULL).

The new code counts up or down from current_y in both softwrap mode and
non-softwrap mode.  In non-softwrap mode, it also avoids the double loop,
since go_back_chunks() and go_forward_chunks() keep the filestructs they
operate on from going to NULL.

Use go_back_chunks() to adjust edittop, instead of special casing
the computation of goal when softwrapping.  Now softwrap mode and
non-softwrap mode will behave the same way when edittop can be
partially scrolled off the screen, which is forthcoming.

(Note that the top line of the screen can't be partially scrolled
yet, so we have to work around that for now.)

Use go_back_chunks() and go_forward_chunks() to adjust edittop and to
move up or down to the scrolled region before updating the rows there.
Now softwrap mode and non-softwrap mode will behave the same way when
we can scroll the top line of the screen partially off the screen,
which is forthcoming.

(Note that the top line of the screen can't be partially scrolled yet,
so we have to work around that for now.)

Not drawing a line on a row if we're on the top row and scrolled down,
or if we're on the bottom row and scrolled up, will only work properly
if the line on that row takes up only that row.  The latter might not
be the case in softwrap mode: if the line occupies multiple chunks and
begins on that row -- in that case none of the chunks would be drawn.

The old name made it sound as if it didn't apply in softwrap mode.  But
it does: in softwrap mode a line needs updating  when the mark is on.

In softwrap mode, nano doesn't horizontally scroll lines at all, so in
this case get_page_start() should always return zero.