algorithm validation

[mdsumner]

Stuff to consider/check

• [ ] merge rearcut JS implementation with this package
• [ ] set up tests that ensure the design claims are met
• [ ] writer converters from known data, like minimal_mesh and similar with more holes

tests

• [ ] coordinate order doesn't matter (is this claimed?)
• [ ] duplicates don't matter https://github.com/mapbox/earcut.hpp/issues/7#issuecomment-119623474
• [ ] test with mixes of ring order, mixes of start/end duplication
• [ ] test with holes outside of islands

from https://github.com/hypertidy/decido/issues/5

[mdsumner]

also see #17