Fixed that annoying floating point test issue

Floating point comparisons are always so much fun. Apparently the machines at Travis-CI generate slightly different results (imagine that), which caused the test to fail in CI, despite passing on the development system.
Added Polyline#spokes
Added Polyline#right_bisectors

The opposite of left-bisectors
Added Polygon#spokes

Polyline#spokes doesn't properly handle concave polygons