NF: Find the closest vertex on a sphere for an input vector.
BF + NF: Implement find_closest for Hemisphere.
Account for antipodal symmetry as appropriate for Sphere/Hemisphere.
TST: Demonstrate that this is scale-invariant.
PEP8: whitespace between functions.
Merge pull request #483 from arokem/find_closest

NF: Find the closest vertex on a sphere for an input vector.