Add a tool

If you don't like the default arguments to a grep tool or you want to add a new one, just add/replace the key to g:grepper:

let g:grepper = {
    \ 'tools': ['pt', 'git'],
    \ 'pt': {
    \   'grepprg':    'pt --nocolor --nogroup',
    \   'grepformat': '%f:%l:%m',
    \   'escape':     '\+*^$()[]',
    \ }}