Submit given completions to fishshell

[SonYBell]

Hi, and thanks for this great project.

Fishshell loves completion contributions. Instead of proving custom ones, submitting completions to the main project would be way nicer!

Best

[faho]

Speaking with my fish-shell contributor hat on, here's what might still be of interest:

• rake
• cap
• git-svn

Neither of them are particularly large, and git-svn would need to be rewritten as a subcommand-completion (for git svn, not git-svn - I don't have the latter on my system).