Feature/branch scripts

First of all, great tool. We've been using it and are pretty happy with it.

This PR makes it possible to call different build and publish scripts based on which branch is firing the webhook. One of the use cases would be to build and publish a ```develop``` branch to a staging environment with simple authentication, while ```master``` would trigger a build and publish to a production environment.

The other commit makes it possible to use Jekyll Hook with branch names with a slash in them, like ```feature/pretty_map```.
What is the reasoning behind this change and the one on line 40?