Allow the user to search in a help text with ^W and M-W.

Achieve this by not writing the help text directly to the screen
but first writing it to a temporary file and then opening this file
in a new buffer, and treating it specially: the normal file-reading
feedback is suppressed, the titlebar shows the headline of the text,
the cursor is hidden, and the menu is limited to just the up and down
movements and searching.

This fulfills https://savannah.gnu.org/bugs/?28994

.
Signed-off-by: Rishabh Dave <rishabhddave@gmail.com>

File formats, appending and prepending, and backups are not available
when --enable-tiny is used, so prevent all relevant pieces of code from
getting compiled.  And correct two misspelled ENABLE_TINY to NANO_TINY.

This also groups ^I and ^M together, and cutwordleft and cutwordright
(when they are bound).  It furthermore makes that less pairs are now
mixed and instead consist of either two Ctrl or two Meta combos.  In
short: it looks better in the default config.  The only sacrifice is
that Verbatim is now split off from the other "inserting" keys.

When UTF-8 is available, use actual arrows instead of untranslated words
to indicate the cursor keys in the search history, as is done elsewhere.

The interval 2013-2017 for the Free Software Foundation is valid
because in those years there were releases with changes by either
Chris or David, and the GNU maintainers guide advises to mention
a new year in all files of a package, not just in the ones that
actually changed, and be done with it for the rest of the year.

Also, M-A is far more mnemonic for setting the mark than ^6 or ^^,
so it's better to try and teach the user that.

On some terminal emulators, Ctrl+Home and Ctrl+End produce special
keycodes, distinct from plain Home and End.  Make the users of those
emulators (and of the Linux console) glad by making ^Home and ^End
do the obvious thing, and the combinations with Shift too.

When UTF-8 is available, use actual arrows instead of untranslated words
to indicate the cursor keys.  This was already done for the combinations
with Ctrl but not yet for the plain cursor keys.

The unshifted shortcuts are easier to type, and also less confusing in
my eyes.  Putting them first means they get shown in the help lines,
and get listed first in the ^G help text.

(I would also like to put ^- first instead of ^_ (because the latter
is hard to see when using the default inverse video for shortcuts),
but on several terminal emulators Ctrl+- reduces the font size.)

Making ^Up and ^Down go to top and bottom row in the file browser
complements and completes the behavior of ^Left and ^Right.

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.

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.

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.

The platform's default char type might be signed, which could cause
problems in 8-bit locales.

This addresses https://savannah.gnu.org/bugs/?50289

.
Reported-by: Hans-Bernhard Broeker <HBBroeker@T-Online.de>

Now that we pull in the gnulib regex module, we can assume it exists.

Also, avoid a warning with with --enable-tiny --enable-browser.

In path names and file names, 0x0A means an embedded newline and
should be shown as ^J, but in anything related to the file's data,
0x0A is an encoded NUL and should be displayed as ^@.

So... switch mode at the two main entry points into the "file system"
(reading in a file, and writing out a file), and also when drawing the
titlebar.  Switch back to the default mode in the main loop.

This fixes https://savannah.gnu.org/bugs/?49893.

Also, swap the logic around, to use less braces.

There is no need for a counter, nor an old counter to compare it with.

Instead compute directly whether we're at a softwrapped part or not.

(The variable 'pletion_line' is not conditionalized with this option, as
it would become messy.  The compiler will probably be able to elide it.)

When using --enable-tiny, it is not possible to use --enable-wordcomp,
because the word completion function uses the undo system.

Executing the 'complete_a_word' function will search from the start
of the current buffer for entire words that begin with the fragment
that is before the cursor, and will complete this fragment to the
first word that is found.  Each consecutive call of 'complete_a_word'
will search for the next matching word and will complete the fragment
to that.  By default the function is bound to the ^] keystroke.
Signed-off-by: Sumedh Pendurkar <sumedh.pendurkar@gmail.com>
Signed-off-by: Benno Schulenberg <bensberg@justemail.net>

Reported-by: Sumedh Pendurkar <sumedh.pendurkar@gmail.com>

It can be activated with --linenumbers on the command line or with
'set linenumbers' in a nanorc file, and it can be toggled with M-#.
Signed-off-by: Faissal Bensefia <faissaloo@gmail.com>
Signed-off-by: Benno Schulenberg <bensberg@justemail.net>

Instead of figuring them out from the string.  This is possible
because those dedicated editing keys cannot be rebound anyway.

This fixes https://savannah.gnu.org/bugs/?49058 reported by Rishabh Dave.

And also case-sensitive searches, backward searches, and searching again.

This fixes https://savannah.gnu.org/bugs/?48987.