add ctrlp.vim

See also:
* http://kien.github.io/ctrlp.vim/
* https://news.ycombinator.com/item?id=6372461
* http://andre.arko.net/2013/09/11/vim-is-the-worst-editor/
add :Qargs plugin

See:
* http://stackoverflow.com/questions/5686206/search-replace-using-quickfix-list-in-vim/5686810#5686810
* http://andre.arko.net/2013/09/11/vim-is-the-worst-editor/
* https://news.ycombinator.com/item?id=6372461
Git-ignore /.netrwhist