Icosalattice

Fixes
- moved functions involving peel coordinates from the playground script where I had made them to the IcosahedronMath module so they can be imported (although they will end up elsewhere later once I organize them)

Features
- added "peel coordinates" system, which says how far in the L and D directions a point is from its ancestral starting point, if the half-peel is deformed into a square with L and D orthogonal
- get point code directly from coordinates without recursive ancestry lookups, instead using the peel coordinates

Features
- added ability to get which icosahedron face a point is located on

- initial release
- basic math about icosahedron vertices, coordinate conversion
- some basic tests