Pymox

* Reworks `README`
* Adds `to_be`, `called_with`, `and_return` and `and_raise`
* Methods `stubout` and `stubout_class` now return the stubs
* Adds global_unset_stubs and global_verify to the Mox metaclass
* Adds minimal `pytest` support
* Adds requirements file to build docs
* Adds `furo` as docs theme
* Adds `create`, `expect` and `stubout` context managers

**Full Changelog**: https://github.com/ivancrneto/pymox/compare/v1.1.0...v1.2.1