Py-pde

This release is the first one supporting multiprocessing using MPI. Details are discussed in [the documentation](https://py-pde.readthedocs.io/en/latest/manual/performance.html#multiprocessing-using-mpi).

What's Changed
* Added basic MPI support for multiprocessing by david-zwicker in https://github.com/zwicker-group/py-pde/pull/280
* Added conservative double divergence for spherical grids by david-zwicker in https://github.com/zwicker-group/py-pde/pull/274
* Allow selecting multiple fields from a collection by david-zwicker in https://github.com/zwicker-group/py-pde/pull/276
* Bumped required numpy version to 1.22 by david-zwicker in https://github.com/zwicker-group/py-pde/pull/277
* Fixed a bug when same Interrupt object was used in different trackers by david-zwicker in https://github.com/zwicker-group/py-pde/pull/278

**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.21.0...v0.22.0

What's Changed
* Added FieldCollection.from_dict classmethod by david-zwicker in https://github.com/zwicker-group/py-pde/pull/262
* Allow specifying boundaries by name by david-zwicker in https://github.com/zwicker-group/py-pde/pull/269
* Refactored tracker intervals by david-zwicker in https://github.com/zwicker-group/py-pde/pull/267
* Improve parsing of sympy expressions by david-zwicker in https://github.com/zwicker-group/py-pde/pull/264
* Improved storage of information about adaptive time stepping by david-zwicker in https://github.com/zwicker-group/py-pde/pull/265
* Replace numpy.inf with math.inf by david-zwicker in https://github.com/zwicker-group/py-pde/pull/268
* Broadcast scalar results in `evaluate` by david-zwicker in https://github.com/zwicker-group/py-pde/pull/266
* Fixed type issue in Parameterized by david-zwicker in https://github.com/zwicker-group/py-pde/pull/261


**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.20.0...v0.21.0

What's Changed
* Explicit treatment of normal boundary conditions by david-zwicker in https://github.com/zwicker-group/py-pde/pull/250
* Improved operators for `SphericalSymGrid` by david-zwicker in https://github.com/zwicker-group/py-pde/pull/249
* Improved type hints and docs by david-zwicker in https://github.com/zwicker-group/py-pde/pull/248


**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.19.2...v0.20.0

What's Changed
* Treat NaN in state space in adaptive time stepping by david-zwicker in https://github.com/zwicker-group/py-pde/pull/239
* Added improved adaptive stepper for runge-kutta method by david-zwicker in https://github.com/zwicker-group/py-pde/pull/240
* Enhance docs for the solve method of class pde.pdes.base by lmenou in https://github.com/zwicker-group/py-pde/pull/241
* Improved documentation by david-zwicker in https://github.com/zwicker-group/py-pde/pull/242
* Added a Counter class for a better implementation of JIT_COUNT by david-zwicker in https://github.com/zwicker-group/py-pde/pull/243
* Added method to show mathematical representation of boundary conditions by david-zwicker in https://github.com/zwicker-group/py-pde/pull/245
* Added user-defined boundary conditions by david-zwicker in https://github.com/zwicker-group/py-pde/pull/246
* Improved implementation of UserBC to handle more cases by david-zwicker in https://github.com/zwicker-group/py-pde/pull/247

New Contributors
* lmenou made their first contribution in https://github.com/zwicker-group/py-pde/pull/241

**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.19.1...v0.19.2

What's Changed
* Remove NaN values before smoothing 1D data by david-zwicker in https://github.com/zwicker-group/py-pde/pull/237
* Improved edge cases of SmoothData1D by david-zwicker in https://github.com/zwicker-group/py-pde/pull/238


**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.19.0...v0.19.1

What's Changed
* Removed coordination normalization from transform calls by david-zwicker in https://github.com/zwicker-group/py-pde/pull/214
* Removed temporary pin of pytest version by david-zwicker in https://github.com/zwicker-group/py-pde/pull/215
* Removed unnecessary field copy from ConsistencyTracker by david-zwicker in https://github.com/zwicker-group/py-pde/pull/216
* Removed CartesianGridBase by david-zwicker in https://github.com/zwicker-group/py-pde/pull/218
* Added anti-periodic boundary conditions by david-zwicker in https://github.com/zwicker-group/py-pde/pull/219
* Fixed a bug in the adaptive stepper that occured when error vanished by david-zwicker in https://github.com/zwicker-group/py-pde/pull/223
* Refactored explicit stepper to be structured more clearly by david-zwicker in https://github.com/zwicker-group/py-pde/pull/224
* Updated requirements by david-zwicker in https://github.com/zwicker-group/py-pde/pull/225
* Allowed creating fields from expressions that cannot be vectorized by david-zwicker in https://github.com/zwicker-group/py-pde/pull/228
* Added `evaluate` function by david-zwicker in https://github.com/zwicker-group/py-pde/pull/231

**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.18.0...v0.19.0