Qpimage

- setup: bump nrefocus from 0.2.0 to 0.2.1

- docs: fix sphinx build
- tests: fix tests due to newer h5py version
- ref: fix numpy 1.20.0 deprecation warnings
- ci: migrate to GitHub Actions
- setup: setup.py test is deprecated

- maintenance release

- maintenance release

- feat: automatically remove 2PI phase offsets when instantiating
a QPImage (The phase offset is estimated from a 1px-wide border
around the image)
- feat: allow to disable the processing of phase data (unwrapping
and correcting for phase offset) using ``proc_phase=False``
when instantiating a QPImage

- docs: minor improvements