SPACalculator - signifcant changes to be closer to the original source

Thanks to @dickermoshe fo pointing out a number of bugs and showing that the SPA code was not true to the original. This now brings it to where it hopefully should have been. Accuracy never drifts over 1.7 ms from the original. This version brings very significant performance improvements over the original. It also leverages caching in the parent AstronomicalCalculator class.

Note: This is very experimental and is subject to change

Author: KosherJava