Py-pde

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

What's Changed

* Changed name of default plotting action from "create" to "none".
* Removed the deprecated names `PolarGrid` and `SphericalGrid`
* Added explicit method to convert coordinates between different systems
* Adjusted tests

**Full Changelog**: https://github.com/zwicker-group/py-pde/compare/v0.17.3...v0.18.0

Fixed bug that prevented many operations on new sympy version 1.10.

Introduced time-dependent boundary conditions and smaller fixes