Linear delta solution forward & inverse kinematics now support per-tower rotation, radius, and arm length offsets.
The forward kinematics haven't been tested because NOTHING calls that method! It seems only to be used in SCARA solutions.
LinearDeltaSolution::get_optional() and ::set_optional() now store tower rotation/radius/arm length.
Forward kinematics method has some comments added to make it a little easier to understand.
Added support for ComprehensiveDeltaSolution heuristic calibration system.