0.39.0

This release collects minor adjustments, but there is also one which makes py-pde compatible with newer versions of matplotlib.

What's Changed

• First variant of a ModelrunnerStorage class by @david-zwicker in #555
• Fixed an import to be compliant with newer matplotlib versions by @david-zwicker in #556
• Improved documentation by @david-zwicker in #558
• Store intermediate state information in case of error by @david-zwicker in #560
• Added better support for forward and backward derivatives by @david-zwicker in #562
• Added forward difference for vector fields on spherical grids by @david-zwicker in #563
• Added forward/backward derivatives for divergence on Cartesian grid by @david-zwicker in #564
• Cleaned up some defintions of operators by @david-zwicker in #565
• Added example for how to use storages by @david-zwicker in #568

Full Changelog: 0.38.0...0.39.0