Implementation of sectored traversal, transition from angular -> polar

[cgyurgyik]

Sectored Sphere Traversal (#102): (WIP)

• Removed min_bound, max_bound.
• Add SphereBounds.
• Add simple hemisphere tests.
• Add simple first quadrant tests.

Other:

• In the initialization phase, if the squared euclidean distance is zero, we determine the voxel ID is zero and can skip any obtuse line segment checks.
• Generalize angular voxel ID initialization.
• Change angular to polar when describing the XY plane voxels.
• Add tests by Youhan for tangential hit bug (DISABLED for now).
• Add make keyword to run benchmarks, tests documentation.
• Add 'ing' to circleci .yml file.

[cgyurgyik]

@ak-2485 , @nukenukenukelol I've implemented a prototype of the segmented traversal, with a few tests. Please take a look, and criticize. Edit: I've reverted this for now. I was under the impression we would be using voxel boundaries, but I am told this is no longer the case.