Use ripgrep to speed up CtrlP

Ripgrep is even faster than The Silver Searcher (ag): https://blog.burntsushi.net/ripgrep/
This makes it a nice fit for CtrlP
Here's how to set up CtrlP to use Ripgrep if it is on the path:

First install ripgrep (brew install ripgrep on OSX)

Add this to your .vimrc

if executable('rg')
  set grepprg=rg\ --color=never
  let g:ctrlp_user_command = 'rg %s --files --color=never --glob ""'
  let g:ctrlp_use_caching = 0
endif