* 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
AMParamStmt was not calling to_gerber on each of its primitives
on his own to_gerber method. That way primitives that changes after reading,
such as when you call to_inch/to_metric was failing because it was
writing only the original macro back.
PCBmodE uses a standard but probably undefined behaviour issue
on Gerber where it defines circle apertures with a single modifier
but leaves a trilling 'X' after it. 'X' is modifiers separator but
when there is only one modifier the behaviour is undefined.
For parsing we are just ignoring blank modifiers.
Test updated to catch this case.
