v0.1.5

This release contains numerous improvements and new features. The most important ones are listed below:

1. The public API was cleaned. The docstrings and the documentation pages were improved. Examples scripts were simplified and reorganized. The naming of instances and classes was also improved by avoiding unnecessary abbreviations as well as avoiding repetition of from the upper hierarchy level.
2. A 2DOF speed controller was refactored and the design notes were added to the documentation. As a special case, the controller can be parametrized as a standard PI controller.
3. A 2DOF PI current controller was refactored and the design notes were added to the documentation. Now, the same base class can be used for both synchronous and asynchronous machines. As a special case, the controller can be parametrized as a standard PI controller.
4. The default machine parameters were removed from the system models and as well as from the control algorithms. Instead, this data is now provided in the example scripts. This change is expected to reduce the risk of user errors.
5. Saturation models were simplified and generalized. The SynchronousMotorSaturated class can be now used with both analytical saturation models and look-up tables. The detailed examples of how to parametrize saturated motor models were moved to the example scripts.
6. To reduce overlapping code, sensored observers were merged with sensorless observers. Design notes were added to the documentation.