nano: Update to 6.4

nano: Update to 6.4

For details see:
https://www.nano-editor.org/news.php

"Changes between v6.3 and v6.4:
------------------------------

Benno Schulenberg (24):
      bump version numbers and add a news item for the 6.4 release
      display: remember text and column positions when softwrapping a line
      docs: concisely describe how the linter behaves
      docs: remove the two notices about the changed defaults
      docs: rename README.GIT to README.hacking, so it's clearer what is meant
      docs: stop mentioning the obsoleted keywords that were removed
      files: designate the root directory with a simple "/", not with "//"
      formatter: instead of leaving curses, use full_refresh() to wipe messages
      gnulib: update to its current upstream state
      help: reshuffle two shortcuts so that more help-line items are paired
      options: stop accepting -z, as --suspendable has been dropped too
      rcfile: remove five obsolete or deprecated keywords
      syntax: default: do not colorize a square or angle bracket after a URL
      syntax: perl: add missing keywords, and reduce the length of some lines
      syntax: python: mention an alternative linter in a comment
      tweaks: add a missing word to a news item
      tweaks: add a translator hint
      tweaks: improve a comment, and reshuffle two functions plus some lines
      tweaks: put each regex on separate line, to better show many keywords
      tweaks: rename a variable, to not be the same as a function name
      tweaks: rename two variables, to not contain the name of another
      tweaks: reshuffle a description and rewrap another
      tweaks: reshuffle a few lines, to group things better
      version: condense the copyright message, to not dominate the output

LIU Hao (1):
      build: ignore errors from `git describe`"

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Reviewed-by: Peter Müller <peter.mueller@ipfire.org>