share: add option to share bookmarks
This patch adds the -B/--bookmarks option to the share command added by the
share extension. All it does for now is create a marker, 'bookmarks.shared',
that will be used by future code to implement the sharing functionality.
highlight: ignore Unicode's extra linebreaks (
issue4291)
Unicode and Python's unicode.splitlines() treat several extra legacy
ASCII codepoints as linebreaks, even though the vast bulk of computing
and Python's own str.splitlines() do not. Rather than introduce line
numbering confusion, we filter them out when highlighting.