It does not update anything -- it just picks a new point from
where to start displaying the buffer.  All actual updating of
the screen is done by edit_refresh() and edit_redraw() and such.

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/?49099,
and fixes the unreported corresponding bugs for
<End> and <Del> and typing extra characters.

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

Mentioning "GNU nano" instead of "This program" and referring to the
website instead of to a postal address.

Leave the optimization of actual screen writes to ncurses.

Add the keycodes and routines to allow the user to forego setting the
mark explicitly (with M-A / ^6) and instead quickly select a few words
or lines by holding down Shift together with the movement keys.

(Some combinations with Shift are swallowed by some terminal emulators.
To work around some of those, the combinations Shift+Alt+Left/Right work
as Shift+Home/End and Shift+Alt+Up/Down work as Shift+PageUp/PageDown.)

This fixes https://savannah.gnu.org/bugs/?48751 reported by Andrew Ho.

This also fixes compilation when configured with --enable-tiny.

If this breaks your build, please send report or instructions or patch.

This fixes https://savannah.gnu.org/bugs/?48660.

Straightforward code is more important than the tiniest possible binary.

Also adjust some comments and rename a variable.

For horizontal scrolling, it is not the /desired/ column position that
is relevant for determining whether a line needs to be redrawn after a
cursor movement, but the /actual/ column positions before and after.

This fixes https://savannah.gnu.org/bugs/?48627,
and fixes https://savannah.gnu.org/bugs/?48629.

Having two unneeded parameters in the tiny version is acceptable --
the code gets so much more readable.

Leave the rest of any escape sequence to be processed normally, which
should be possible because those characters are all in ASCII range.

This fixes https://savannah.gnu.org/bugs/?48318.

There is no need to specially flag a function key or editing key --
the keycode is indication enough in itself: outside of byte range.

And instead of using two key types, just use a bool to indicate whether
a keystroke involves Meta.

A keycode is either already in byte range (so there is nothing to do)
or it is not and it shouldn't be (so there is nothing to do either).

After initialization, the type of a key is never used nor needed
(other than for meta keys).

Those lines don't exist in that mode -- the relevant subwindows are
smaller, or have been made smaller just before.

This fulfills https://savannah.gnu.org/bugs/?48154.

And hard-bind the keys Ctrl+Up and Ctrl+Down to these functions.

Unlike the paragraph-jumping code, these new functions disregard
any indentation, treating only blank lines as separators.  They
also do an automatic smart home when that option is set.

This fulfills https://savannah.gnu.org/bugs/?48291.

This allows the user to specify which other characters, besides the
default alphanumeric ones, should be considered as part of a word, so
that word operations like Ctrl+Left and Ctrl+Right will pass them by.

Using this option overrides the option --wordbounds.

This fulfills https://savannah.gnu.org/bugs/?47283.

When we get a ^J as verbatim input, it is not possible to include it
into the file buffer or the prompt answer, because this would mean
adding an encoded null to the buffer or answer, and that is not what
the user intended.  One option would have been to simply ignore a ^J
in verbatim input.  But the choice has been made to act the same way
as when the ^J (0x0A) is found in the file data: start a new line.

That is the same response as to the Enter key, yes -- but the code
for the Enter key is ^M (0x0D), not ^J.  So, to be more precise,
rename the relevant variable from 'got_enter' to 'got_newline'.

Use knowledge of UTF-8 instead of converting to wide characters first.

Any control character is represented by a ^ plus an ASCII character.

Instead of showing the upper control codes like this:

   ^À ^Á ^Â ^Ã ^Ä ^Å ^Æ ^Ç ^È ^É ^Ê ^Ë ^Ì ^Í ^Î ^Ï
   ^Ð ^Ñ ^Ò ^Ó ^Ô ^Õ ^Ö ^× ^Ø ^Ù ^Ú ^Û ^Ü ^Ý ^Þ ^ß

show them like this:

   ^` ^a ^b ^c ^d ^e ^f ^g ^h ^i ^j ^k ^l ^m ^n ^o
   ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^{ ^| ^} ^~ ^=

The lower control codes continue to be shown like this:

   ^@ ^A ^B ^C ^D ^E ^F ^G ^H ^I ^J ^K ^L ^M ^N ^O
   ^P ^Q ^R ^S ^T ^U ^V ^W ^X ^Y ^Z ^[ ^\ ^] ^^ ^_

The representation of DEL (0x7F) continues as ^?.

Further, use knowledge of UTF-8 to avoid a roundtrip through
wide characters.

By moving the test for the only situation where do_comment() does nothing
(when only the magic line is selected) further up front, the add_undo()
can be called before the commenting/uncommenting starts and two variables
and an extra function are made unnecessary.