[WIP] contrib: localvimrc

Is anyone at all using https://github.com/neovim/neovim/tree/master/contrib/vim-addon-local-vimrc ?
And forgot a thing: with this code *each time buffer is opened or loaded* path gets a new entry. Thus Vim will quickly become slow when searching using built-in functionality. Thus I would suggest two options:

1. Do not use `let &path`, use `let &l:path`.
2. Guard the whole construct with `if !exists('s:srcroot`)`.
3. Guard the `let &path` line with `if stridx(&path, escape(s:srcroot, '\,').'/**') == -1` (better to include escaping and `/**` into `s:srcroot`).