Allow site-specific .vimrc extensions

* Load files of the format ~/.vimrc.*
* Add an empty .vimrc.local file (so that vim doesn't complain)

Signed-off-by: Tim Ekl <lithium3141@gmail.com>
Add an empty .zshrc_local

In keeping with the recent empty .vimrc.local, keep an empty local zshrc
extension file so that zsh won't complain with the default .zshrc
provided here. (It's still ignored, so changes shouldn't be committed.)

Signed-off-by: Tim Ekl <lithium3141@gmail.com>