Changes

KeplerianFromStateVectors() improvements

Fixes my janky method of dealing with retrograde orbits by properly
using retrograde equinoctial elements for retrograde cases.

Adds quite a few tests.

Fixes the random forward-and-back tests to be pseudo-random to eliminate any
pseudo-random failures.

Fixed an issue in Clamp2Pi that could result in small negative values
annoying returning exactly 2Pi instead of [0,2Pi)

Now using an exact EPS value instead of the one I historically had been
using for years that was rounded off to be slightly too small.
 (commit: 4851e88)