Especially: get rid of the "Up: (dir)" link that points nowhere.

Also, add a horizontal line before the final Table of Contents.

This fixes https://savannah.gnu.org/bugs/?51208.

Also, harmonize some configure-option descriptions,
add a slash after a subdir, and fix a typo.

Also, add two missing configure options, and frob some other things.

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.

Furthermore, change an item header into a question, swap two items,
and tweak the formatting a bit.

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.

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.

And slightly change the existing one for normal users.

And modify a few wordings too.

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

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

Also, add two cross references: one in words, and one with a link.

Also, remove the special "+line,column" argument from among the options,
since it isn't an option -- put it in a separate paragraph instead.

If the system on which nano is configured does not have the 'makeinfo'
program installed, the prebuilt and packaged nano.info and nano.html
should nevertheless be installed.

Also, the TEXINFOS primary has built-in rules for generating HTML files
from the texinfo sources, so an explicit rule is not needed.

This indirectly addresses https://savannah.gnu.org/bugs/?49969.

They are not documentation, they are functional elements of nano.

There are just a handful of source files for the documentation --
it is wasteful and cumbersome to have these in separate directories.

Also: remove the French man pages -- they are too far out of date.
(And anyway, we should acquire a general framework for translating
the documentation.)

Signed-off-by: Arturo Borrero González <arturo@debian.org>