Hoisted `bore()`

Eliminated use of `polyhedron` in favor of a `linear_extrude() polygon()`
Minor lint corrections

Bunch of fixes / improvements

1. Improved preview by adding 0.001 expanded tolerance to all holes cut
2. Corrected "cross" shape; should be two intersected pill shapes instead of four circles
3. Added countersink support to all shapes, and added countersink size params
4. Corrected deformation of sphere to seed_depth, and added depth support to half-moon and cross shapes
5. Corrected half-moon shape
6. Added units to params
7. Fixed marshalling of params into library

Build process now includes sample stl