Tracker limit angle update

Minor revision to allow adjustment of tracker rotation limit

Single axis tracking update

Several errors were discovered in the SAT algorithm that have been addressed here.
SAT ground clearance is now set by C = hub height (clearance at tilt = 0). This value must be > 0.5 to avoid errors
Row spacing may be set with either D (gap space between modules) or rtr (row to row spacing).

Initial stable release

BifacialVF stable release