Implement MethodHandlePrototype and a couple RuntimePolicies

- finish implementing MethodHandlePrototype
  * add getters and setters
  * implement a reasonable constructor
  * split bake into owner resolution and method handle creation
- add a couple implementations of RuntimePolicy:
  * PassthruPolicy, which always directly returns handle from
    the prototype
  * LoggingPolicy, which prints to stderr all methods being intercepted
    and passes the call to another policy