WIP: Added InvokeBehavior and a default implementation of it

This is the direction I am going in for the "AutoData" feature. Having an InvokeBehavior will allow you to keep all the awesome error and async handling going on in the Invoke CaseBehavior class, but gives you the flexibility to inspect the case method and determine if more work needs to be done.

I suspect that was the original intention of CaseBehavior was supposed to be, but I didn't feel comfortable copy/pasting the Invoke class and modifying it with what was needed. This feels a bit more natural.

I'd love to get your thoughts on this line of thinking before I go further...