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}-*`
* `--tag-relative` makes the tags file output tag file locations relative to the project root.
* `-L -` is the list of files piped in
* `-f"$dir/$$.tags"` builds the tag file location as project_root/process-id.tags
* `--languages=-javascript,sql` excludes javascript and sql files from being tagged. The reason is that the quality of the tags for those is low.