Scara-Kinematics for Marlin

It has been developed as a Marlin fork 2 years ago by Quentin Harley, but never been integrated into master tree. Now, I integrated it into fork of actual-master tree. It did it the same style, like delta-kinematics has been integrated. Without switching #ifdef SCARA on, there should be no changes visible.

Please feel free to give comments.

Hopefull it will now find its way into master tree, because SCARA-printers are uprising.

Kind Regards,
Yogi