Switch from rvm to chruby

This should pick up `.ruby-version` and `.ruby-gemset` files in
directories. You'll need to manually compile/install rubies, commands
are on the wiki:
https://github.com/postmodern/chruby/wiki#installing-rubies
Update Mutt config

- Use an arrow in the index (supported in the default Arch console font)
- Unbind 'x'
- Organize mailing lists
Add more aliases

- various git aliases (shadowing things I don't use like ghostscript)
- more vagrant aliases
- swi-prolog → pl
- ranger (file browser) → r
- list files in one long line → l1
Organize aliases

Also: remove some unneeded 'open' aliases
Manage vim plugins with vim-plug

- Install with :PlugInstall
- Update with :PlugUpdate
- More info https://github.com/junegunn/vim-plug and
  https://github.com/junegunn/vim-plug/wiki/faq