First `SISUA` stable release:
* Generalized `SingleCellOMIC` data representation based on `scanpy`.
* Add a generalized `SingleCellModel`, allow developing new model faster.
* Native implementation of DCA and scVI using `tensorflow` and `tensorflow_probability`.
* Switch to tensorflow-2.0 for the more intuitive development process.
* Update `Posterior` class with new analysis
* More distribution support.