Fix 'vimdiff dir1 dir2' arguments handling.

Escape each argument, so for example paths with spaces work.
Update C dictionary.
Improve Bazaar settings/syntax.

- move settings were they belong
- improve syntax: use internal support for diff highlighting and fix
  spelling to only be applicable for the commit message part of the
  buffer
Update plugin: vcscommand.
Update plugin: bufexplorer.
Update colorscheme: lucius.
Update documentation.

Switch install instructions from Bazaar to Git.