Optionally install tensorflow dependency
Optionally install tensorflow dependency

Additionally:
- Set long_description equal to the readme.
   - Example: https://test.pypi.org/project/dm-reverb/0.1.0rc0/
- Refactor to be modular.
PiperOrigin-RevId: 323599945
Change-Id: Ia9faf886ee71e9214b3fcd461797d7230eb7a36c

deepmind/reverb,deepmind/reverb,deepmind/reverb,deepmind/reverb