Public Domain Involute Parameterized Gears: Powered Up

This is an update to the Public Domain involute Gears library by @3dexplorer, with optimisations by @zkarcher.

This library provides a module called gear(), which makes ordinary gears, helical gears (twisted like a screw), inner gears (teeth on the inside), and partial gears (a wedge rather than a full disk). It also provides a module called rack(), which creates a bar with teeth that will mesh with the gears (also optionally helical gears), so you can generate a rack and pinion set.

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