Add support for config phase

I think beat is awesome and was pleasantly surprised to find providers implemented as a feature. I was more surprised, though, not to find support for provider configuration as in AngularJS. I'm sure it's something you just haven't gotten to yet. I took the liberty to add it!

Now, I'm not entirely sure it works the same as AngularJS, but it is certainly close enough for my purposes. Essentially, before any function registered via the run method is invoked, all functions registered via the config method are invoked with their respective provider dependencies.