change `ctrlp_user_command` to use git listing command

Much faster when running ctrlp for the first time in a session. Does not scan
untracked files, and is not aware of submodule files.

vim/vimrc

@@ -313,6 +313,13 @@ let g:syntastic_auto_jump = 1
 
 """"""""" CtrlP
 let g:ctrlp_working_path_mode = 'rw'
+let g:ctrlp_user_command = {
+  \ 'types': {
+    \ 1: ['.git', 'cd %s && git ls-files'],
+    \ 2: ['.hg', 'hg --cwd %s locate -I .']
+  \ },
+  \ 'fallback': 'find %s -type f'
+\ }
 
 
 """"""""" Vim Markdown