* Migrate to pytest
All tests were update to use pytest.
Tests were alse black formatted. Eventually all code
will be black formatted but need to merge some PRs first.
- 'clear' polarity primitives no longer erase background
- Added aperture macro support for polygons
- Added aperture macro rendring support
- Renderer now creates a new surface for each layer and merges them instead of working
directly on a single surface
- Updated examples accordingly
this incorporates some of @chintal's layers.py changes
PCB.from_directory() simplifies loading of multiple gerbers
the PCB() class should be pretty helpful going forward...
the context classes could use some cleaning up, although I'd like to wait until the freecad stuff gets merged, that way we can try to refactor the context base to support more use cases
