Allow to define query as positional argument

[sheerun]

Currently in my configuration I setup let g:grepper = { 'prompt': 0 } and mapping nnoremap <leader>/ :Grepper -query . It would be really nice if I could drop the -query part from mapping (i.e. allow query to be accepted as positional argument to :Grepper, e.g. :Grepper foobar. This could be available as default or an option. Thank you!