Spherical Math/Geometry Improvements

[keithdoggett]

Currently, our implementation of spherical geometries lack lots of geometric predicates/analysis methods, are inefficient (ex. SphericalLineString#crosses? is O(n^2)), and are unstable when geometries have dense features (#212).

TODOS:

• Change the SphericalMath module to improve stability for feature-dense geometries
• Add more methods to SphericalMath so that we can implement geometric methods more easily
• Implement more geometric methods on spherical geometries (contains?, intersects?, union, etc.).

This could be a helpful resource to borrow some ideas from https://spacetelescope.github.io/spherical_geometry/.