new features
- added `parallelogram()`
- improved helical gears, added helical spur gears
- added `Wire.isclosed()`, `wire.unclose()`
- added support for NixOS
- improved documentation and especially the guide
fixes
- finally fixed rendering not working on MacOSX ! 82 special thanks to GenieTim
- fixed minor problem in mesh intersections 73
- fixed boolean operations on closed wires 62 thanks to GlennWSo
- fixed numpy array compatibility issue 85