Fix incorrect regex that didn't accept byte values a-f.

Also ass slicker support for multibyte characters like \ud834dd1e.
Old implementation would have required user to enter \ud834\udd1e which
is not intuitive.
Initial user completion for mentions...
Preserve typed casing for user complete
Merge pull request #17 from cbadke/vocalchat

Fix incorrect regex that didn't accept byte values a-f.