Symlink ~/.vim -> vim entirely.

res/setup.json, vim/autoload
	-Originally, .dotfiles `symlink`'d individual files and
	directories inside `~/.vim/` to their counterparts in `vim/`.
	This was kept in place because it was a slightly brittle system
	that depended on proper script loading order.
	-Fix nevertheless: make it possible to symlink `~/.vim/` to
	`vim` entirely, which is much cleaner (see `res/setup.json`).