This addresses https://savannah.gnu.org/bugs/?48992.

This brings it in line with the other three "flip" toggles.

The option now causes nano to trim trailing whitespace also when
hardwrapping occurs while the user is typing.

If the user uses a single version of nano, they have no need for
--quiet.  If they do sometimes use an older version and don't want
to see the warnings, they can use 2>/dev/null (they could make an
alias for that and put it before the call of nano).

List "browser", "pageup" and "pagedown" in the manuals; the first
because it matches "speller", and the latter two because they are
what these functions are commonly known by.  The names "tofiles",
"prevpage" and "nextpage" are now undocumented, but they are still
recognized by the code, as they match the tags for these functions.

Date and version are updated to match each release, so the user does
not have to wonder whether the man page really describes the binary.

Also remove a bit of superfluous markup.

The new option 'set selectedcolor' applies to marked text, to the
currently selected file in the file browser, and to the highlighted
match during interactive search-and-replace.

And reword them too, so that it is clearer what the mechanism is
for determining which syntax to use for a file.

Rename the corresponding rc-file option too, of course.

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>

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

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

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.

And make the strings after "start=" and  "end=" more readable.

Mention some things that really set nano apart from Pico.
Plus some other small tweaks here and there.

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.

This addresses a followup of https://savannah.gnu.org/bugs/?50362

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Reported-by: Mike Frysinger <vapier@gentoo.org>