Add git template and hooks for automatic ctags

Uses exuberant ctags to automatically generate tags for code in every
new repository. Use `git init` to pull the hooks into an existing
repository, then `git ctags` is alias to run the hooks/ctags script.

Taken from
[tpope](http://tbaggery.com/2011/08/08/effortless-ctags-with-git.html)