Extend get_softwrap_breakpoint() to break softwrapped lines on
whitespace when a flag is set.  This flag is controlled by the new
rcfile option "atblanks".  The '>' characters marking two-column
characters at the edge of the screen are disabled when it's on.

If get_softwrap_breakpoint() can't find whitespace in screen range, it
will break the line on the screen edge.  (In this case, a blank can be
on the last column of the screen, but text can't, so that a blank on the
last column doesn't become invisible and possibly break the display.)

This fulfills https://savannah.gnu.org/bugs/index.php?49959

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Requested-by: Nicholas Boel <axxisd@gmail.com>

spotlight() now displays softwrapped lines chunk by chunk instead of all
at once.  Since softwrapped lines are no longer of constant width, the
latter approach would fail if softwrapping breaks the spotlighted text.

Instead of taking a string, spotlight() now takes the starting and ending
columns of that string.  Also, its handling of softwrapped lines is now
split off into a separate function, spotlight_softwrapped().

Use actual_last_column() to properly adjust the cursor if placewewant
is past the end of a softwrapped chunk.

Add the new function actual_last_column() to accomplish this.

get_chunk_row() and get_chunk_leftedge() now become wrappers around
get_chunk(); the latter is only used directly in place_the_cursor()
when we need to get both the row and the leftedge.  get_chunk() now
uses the proper formula to implement varying chunk width.

Since chunk width now varies, place_the_cursor() sets the x position
relative to the leftedge in a different way that works regardless
of chunk width, update_softwrapped_line() loops until it gets all
softwrap breakpoints instead of calculating the full length in
advance and getting one full row at a time, the chunk iterators
now count leftedges instead of rows, and fix_firstcolumn() does a
full recalculation of the chunk that firstcolumn is on instead of
simply shifting it back.

Also, in update_softwrapped_line(), when a line's softwrap breakpoint
is before the last column of the edit window, a ">" is now added to
the end of it.

The workaround in place_the_cursor() for when two-column characters
straddle the edge of the screen is removed, as it's no longer needed
now that chunks end before such characters.

Furthermore, do_home() and do_end() use xplustabs() instead of
placewewant again when calculating the leftedge, since placewewant
refers to a column that may or may not be available (if it's not,
the cursor will be placed wrongly).  Make get_edge_and_target() use
xplustabs() instead of placewewant for the same reason; this also lets
us simplify get_edge_and_target(), since xplustabs() will never be
greater than strlenpt().  Finally, since do_end() now has to calculate
rightedge as well as rightedge_x, use the former to implement the same
time-saving optimizations as in do_home().

The cursor is not yet adjusted when we try to go directly to a column
past the end of a softwrap breakpoint, and placewewant handling in the
vertical movement code is not yet adjusted for varying chunk lengths,
but fixes for these are forthcoming.

This fixes https://savannah.gnu.org/bugs/?49440.

get_chunk_row() replaces the formula "column / editwincols".

get_chunk_leftedge() replaces "(column / editwincols) * editwincols".

get_last_chunk_row() replaces "strlenpt() / editwincols".

get_last_chunk_leftedge() replaces "(strlenpt() / editwincols) * editwincols".

This prepares us for any changes in those formulas, and for more such
functions later.

The new function find_softwrap_breakpoint() returns the column number
of the last position in screen range where we can wrap the given text
without breaking a two-column character in half (as was done until now).
The returned column number is the leftedge of the next softwrapped chunk.

If the end of the text is reached while searching for a wrapping point,
the parameter end_of_line is set to TRUE.

The new function get_chunk() uses find_softwrap_breakpoint() to find the
row and leftedge corresponding to a given column of a given line.

If the position of the cursor changes horizontally,
placewewant should change with it.

This fixes https://savannah.gnu.org/bugs/?51407

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

Dereferencing a NULL pointer is never a good idea.

This fixes https://savannah.gnu.org/bugs/?51405

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

Also remove the backslashes from the two syntaxes that contained them.

This completes the fix for https://savannah.gnu.org/bugs/?51370.

Eradicate the need for backslashes, so that the start of the nanorc
manual becomes true, where it says that quotes inside strings don't
need to be escaped.  In the bargain achieve that the empty string
always switches commenting off.

This fixes https://savannah.gnu.org/bugs/?51370,
and fixes https://savannah.gnu.org/bugs/?51394.

This fixes https://savannah.gnu.org/bugs/?51348

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Reported-by: Henrik Karlsson <henrik.karlsson@pulsen.se>
Tested-by: John Wiersba <jrw32982@yahoo.com>

For the man page, encode them properly, and for the Info stuff,
just set the right document encoding.

This fixes https://savannah.gnu.org/bugs/?51369.

The comment marker is not «."» but «.\"», which requires three
backslashes to specify.  Also adjust the documentation.

Also, use proper mark-up for the examples.

This matches the style in the rest of the code.

This avoids some warnings when compiled with -pedantic:

    ISO C forbids comparison of ‘void *’ with function pointer
    ISO C forbids empty initializer braces

When blank_statusbar() has been called, make sure it is effective.

This fixes https://savannah.gnu.org/bugs/?51358.

(Well, redraw them when they're switched on, of course.)  Redraw
them so that they are shown correctly if their content changed.

This fixes https://savannah.gnu.org/bugs/?51356.
and fixes https://savannah.gnu.org/bugs/?51357.

The thing after a 'comment' directive is just a string, not the
name of a program nor a command.

When the active syntax contains a comment command that specifies the
empty string, this should override the default comment of "#" and
should disable the Meta-3 keystroke.

To achieve this, the comment string is now set by default to "#" for
all syntaxes, so that it will be set when no comment command is given
(including for the "none" syntax), and is unset only by explicitly
specifying «comment ""» in a syntax file.

This fixes https://savannah.gnu.org/bugs/?51355

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

And rename a third variable, to match another in its style.

When also --nohelp is active and the terminal is so narrow that the
message that --constantshow displays on the bottom row does not fit,
this causes the cursor to be pushed "offscreen".  Some terminal
emulators don't handle this case correctly, and leave the cursor
in an invisible or mistaken position.  Compensate for this by
moving the cursor back to the start of the row.

This fixes https://savannah.gnu.org/bugs/?51335

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

The extra variable is not needed, because when having read from
standard input, the filename will simply be empty.  It will not
be empty for any other file that was read.

The dash doesn't have to be the first non-option argument: it can
be anywhere among the filenames -- there can even be multiple ones
(but don't mention this explicitly).

Negative arguments of 'fill' are bright green since a few commits.
So now color all valid numeric arguments in that same style -- the
yellow was hard to see on a dark background anyway.

Also, color a zero tabsize as invalid.

This partially adresses https://savannah.gnu.org/bugs/?50998.