Redesign gitignore plugin

- 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 README.md for gi
Merge pull request #175 from jhillyerd/gi-fix
MIT License
Merge pull request #159 from bpinto/mit_license

MIT License
Add peco plugin
Merge pull request #191 from afarrell/add_peco_plugin

Add peco plugin
marks output columnized
Merge pull request #192 from grelkin-features/columnize-marks-output
new folder, themes with readme
New pseudo theme custom-theme
New plugin custom-theme, well the logic is in the theme
moving logic code from theme to plugin
Adding 'on fish_prompt' function
	* will perform the check
	* Will print a message if newer vanilla version detected
Moving function __system_load from theme to plugin
Adding a condition, to keep the version of the custom file in check
Moving where is printed the messages.
Moving some var to global scope. Improve time execution by 2.
Writing the plugin readme.
adding custom-theme in plugins/README
in __load_system now using fish var to find the correct path.