Complete rewrite of the hook lib.

* FIX: Run more than one script per hook. Now for real.
* Simplified DSL. Just pass the name of the scripts.
* To run scripts in background, pass `:&` as a last option, like
  when you use `&` in bash.
* Output background processes to `hooks/log`.
* Put all the scripts in `hooks/bin`. Much more simpler structure.
Merge pull request #5 from jhbabon/new-dsl

Complete rewrite of the hook lib. [closes #3 #4]