X&Y Endstops for Piper 2

* Update* 8/17/2018 - As Alex Balako has pointed out, dragging the endstop over the rail over time may cause issues. Going to redesign to mount to the Y gantry instead to avoid the issue.

*Update* Redesigned to fit on the Y gantry. I am using 2mm Hex Socket Head screws. There is an access hole to fit an allen wrench through to assist in tightening the screws before mounting to the gantry.

Designed for #6-32 Screws and nuts where the part fastens to the X and Y gantries. Hardware to mou