Add peco plugin

MIT License

- removed code that fetches completions frim gitignore.io each time fish
  is started -- makes logins slow!
- gi.load becomes gi.fish, only contains gi function
- add _update_gi_completions.fish: fetches list of completions from
  gitignore.io and places it into ~/.config/fish/completions
- modify gi function to accept update-completions argument

Add Mac OS X compatibility for ranger feature of syl20bnr theme

Correct unicode point in some ReadMe

README of agnoster and bobthefish

removed deprecation warning, vi-mode in fish not yet implemented

Bug fix: Don't auto-set proxy variables if proxy_host unset

- The proxy plugin would create broken environment variables if it was
  enabled but proxy_host was not defined.

- Cache hostname & prompt char
- Use > instead of %