Tidy3d

- New dispersion fitting tool for material data and accompanying `tutorial <examples/Fitting.html>`__.
- (`beta`) Non-uniform Cartesian meshing now supported. The grid coordinates are provided
by hand to `Simulation`. Next step is implementing auto-meshing.
- `DispersionModel` objects can now be directly used as materials.
- Fixed bug to `Cylinder` subpixel averaging.
- Small bugs fixes/added checks for some edge cases.

- Rehash of symmetries and support for mode sources and monitors with symmetries.
- Anisotropic materials (diagonal epsilon tensor).
- Rehashed error handling to output more runtime errors to tidy3d.log.
- Job and Batch classes for better simulation handling (eventually to fully replace webapi functions).
- A large number of small improvements and bug fixes.

[Unreleased]: https://github.com/flexcompute/tidy3d/compare/v2.6.4...develop