Introduce ActorProxy#sync to allow for explicit sync calls
Reuse Actor.async in InstanceMethods#method_missing
Use the proxies for most calls for extra purity
Unify all the class methods into method proxies
Make ActorProxy a subclass of SyncProxy
Override Kernel#tap to use the current Actor
Move the SyncCall-specific code out of Call
Test the behaviour of the proxy_class rather that the class object
Merge pull request #201 from halorgium/call-cleanups

Cleanup usage of Actor class methods by using the method proxies