[WIP] contrib: localvimrc

Is anyone at all using https://github.com/neovim/neovim/tree/master/contrib/vim-addon-local-vimrc ?
A number of localvimrc implementations source localrc files each time buffer is opened. Since my localrc  (https://github.com/thinca/vim-localrc) works fine with `if &filetype is# 'c'` guard it means that defining filetype event here is too late and this code is never executed for the first opened C file.