Added methods initialBearing (initial bearing) and sphericalLawOfCosinesDistance (distance calculated using Spherical Law of Cosines formula).
Added a coordinates validation method.
Using validation method to with all distance methods and bering methods.
Adding error messaging and methods for finding initial and final bearing.
Updated the TODOs in the README.md
Methods for initial and final bearing are complete.
Updated haversine formula
Spherical formula returning NAN
Spherical Law of Cosines method is returning correct results.
Code clean up.