Introduces `git_template` for `git init` templating

Inspired by http://tbaggery.com/2011/08/08/effortless-ctags-with-git.html

* Runs `ctag` on `commit` / `branch` / `checkout`
* Extensible via `~/.git_template.local/hooks/{pre,post}-*`
@mike-burns to be honest, I don't know the first thing about `ctags`, especially what the CLI arguments mean. I wholeheartedly stole the code from http://tbaggery.com/2011/08/08/effortless-ctags-with-git.html, so if there is a better approach, or a better set of arguments to pass in, please be very vocal about what I'm doing wrong.