Add _prepend_path function

Useful for adding items to $PATH from config.fish
Gittip is now Gratipay
Add fish_title.fish to Entropy theme

1. Shows current running process, but only if it's not fish
2. Uses prompt_pwd instead of pwd to provide shortened filesystem path
Show remote SSH hostname in title in Entropy theme
Add budspencer theme

A sophisticated prompt theme.
Merge pull request #4 from tannhuber/budspencer

Add budspencer theme