* Fix some multibyte character completion bugs
- matchLongest now operates on runes instead of bytes so we don't
complete part of a multibyte character.
- Fix some places that mixed string and rune slice indices.
* Fix wrong menu completion for subdirectories
When selecting a menu completion for a file in a subdirectory, the
entire filename would be appended to the command line, even if you had
already typed part of it.
* Escape file completions in menu completion
* Minor refactors and typo fixes
* Fix cmd-menu-complete-back bug
The first use of cmd-menu-complete-back after opening the completion
menu was incorrectly selecting the before-last completion instead of the
last completion.
* Allow completing broken symlinks
Also skip files with stat errors instead of returning.
* Add command to accept current menu selection
This is useful when completing filenames. For example
cmap <c-y> :cmd-menu-accept; cmd-menu-complete
can be used to accept the selected directory completion, then complete
files in the directory.
* Complete command names for map and cmap
