No longer track thumb proximal
Add basic testInteractablePlane example
Add some inline docs on contstrainMovement
Draft testButton example

allows pushing button. This includes an optimization for x and y w/o z,
and vise-versa.
Some getZReposition Cleanup
Refactor to allow z-dimension physics
Add in restoring spring force
Refactor movementConstraints to return corrected values

 - also, only one constraint per, so we don’t need any iterative
solving BS
Add button example
Update constrainMovement docs