Double methods on class with __getattr__

* Resolve bug doubling methods on classes with __getattr__.
* Add regression test
Fix property stubbing

* resolve #45
* Proxy property form the class back to the instance much like we do
* with __call__
* We may want handle generic datadescriptors/non-datadescriptors
Merge pull request #47 from uber/tws-fix-property-stubbing

Fix property stubbing
Merge pull request #44 from uber/tws-double-obj-with__getattr__

Double methods on class with __getattr__
Making mocking callable objects easier

* Fixes #39
* Variables that point to callables can be mocked
* Variables that point to class methods can be mocked
* Variables that point to instance methods can be mocked
* Decorated functions that return callables can be mocked
* Decorated Functions can be mocked