RigidBot Z endstop level adjuster

Z-Level adjuster for the original RigidBot 3D printer. This allows you to fine-tune the Z-level using an M6 bolt by hand. Adapted for use in combination with Peter Stonehams [stainless linear bearing mounts](http://rigidtalk.com/wiki/index.php?title=Linear_Bearing_Mount) and fastened with M4 hex socket bolts with the plastic gantry holders as seen in photos. It is possible that it would work with the original plastic bearing mounts, but I have not tried (please let me know if you do).

I have seen several variants of this concept using smaller screws, but I've found the ones I've tried to be hard to stay consistent; The small screw would vibrate out of position or the level switch would be pushed further down over time. It could also be hard to line up the switch and screw to match.

My design uses a flat bottom M6 screw that will hit the level switch turned at 90 degrees from it's original position. This is easy to do by sight, and the switch itself will not risk being pushed furt