Move verifying doubles into their own module.
Display doubles with the correct class name and use a less generic private attribute for the target.
Move verification functions to their own module.
Verify methods with varargs.
Verify methods with default arguments when not all args are supplied.
Verify methods with default arguments specified positionally and by keyword.
Check unknown kwargs when verifying contract.
Use inspect.getcallargs for method signature checking.
Add InstanceDouble.
Add ClassDouble and move importable testing object into package.