Add a CONTRIBUTING file

Leave the README section in place, as we link to it from all over the
place.
Merge branch 'master' of git://github.com/tpope/vim-pathogen
Silence errors in :helptags

Closes #90.
Always warn on deprecated API
Use fnameescape not `=...`
Merge branch 'master' of git://github.com/tpope/vim-pathogen
Merge branch 'master' of https://github.com/lin134340/vim-plugins
deleted vim-indent-guides submodule