Adds pre-commit hook, hook config script, and relevant README

The pre-commit hook will automatically gofmt code in place, warning you about any changes. It will also fail to commit if either golint or go vet fails.

As git hooks cannot be added to a repository in a way that automatically applies them, `configure-hooks.sh` can be ran to link this pre-commit hook.

@dmp42 @stevvooe 
I agree with your concerns about `golint`, but we're already using it as a gate in our CI setup, so this is no more restrictive. I can also change the `gofmt` semantics to just fail and complain if you prefer that behavior.