Yt-aspect

Maintenance release.

summary
This release bumps the minimum yt version to 4.2 to so that yt_aspect can use the new entrypoints method for registering frontends.

* use yt entrypoints by chrishavlin in https://github.com/data-exp-lab/yt_aspect/pull/18


**Full Changelog**: https://github.com/data-exp-lab/yt_aspect/compare/v0.1.1...v0.2.0

Changes in this Release
- adds a dedicated PVTU frontend
- null element detection with `yt.load('file.pvtu', detect_null_elements=True)`

This release:

* fixes the installation issues
* separates the pvtu and ASPECT functionality into two frontends
* adds CI testing