First release onto PyPI.
Two major changes to `StateSpaceModel` class
- `TransitionModel` and `MeasurementModel` now specified separately. This increases reuseability of classes and stops the unbounded multiplication of `StateSpaceModel` subclasses.
- dependence on random variables for the noise and initial conditions have been separated out into subclasses of `RandomVariable`.
Other improvements:
- Documentation in Sphinx
- Improved test coverage