refactored Proxies test
introduced ProxyException for proxy package
handled proxy returning incompatible type
handled proxy throwing incompatible throwable
extracted common isAssignableTo(Class, Object) to Classes
refactored stubbing test including introduced ProxyException
made incompatible stubbing to throw TestoryException instead of ProxyException
extracted common canReturn/couldReturn/canThrow
prohibited stubbing primitive methods with null
documented compatibility checks during stubbing
merged new design of stubbing/proxying