v0.16

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