Added Fish support

A few differences from Bash version:

1. No `AUTOJUMP_KEEP_SYMLINKS`. Fish always resolves them (for both pwd and cd).
2. No support for file name completion for 3rd party programs. Fish doesn't seem to like when prefix changes in progressive completion requests, so `f__1__/foo/bar` will not complete to `'/foo/bar'`.

This is just a shell wrapper, I did not touch installation scripts as you seem to be actively working on them. Let me know if you need it added. There are a few differences, so install/uninistall messages need changing (source command, init file path).