complete implementation of dynamic.py

[Cyber-JiuJiteria]

    complete implementation of dynamic.py - need requirements of functionality for methods

Originally posted by @Cyber-JiuJiteria in #31 (comment)

[scovetta]

Taking a deeper look here, I think we're fine -- we use dynamic as an abstract base class, so some methods like execute_all are concrete, but no one should be calling execute directly on a DynamicPolicy.

I'm sure there's a way to do this with actual abstract base classes, but I haven't used this before, so not sure if there's a gotcha or what the benefit is over the current approach.