Prusa i3 Rework Endstop Hitter

After upgrading my Prusa i3 rework to an E3D-v6 nozzle and [Tech2C's excellent carriage](http://www.thingiverse.com/thing:547706), I found that the X carriage no longer hit the X endstop.
Initially I solved this with a bulldog clip, but it tended to let loose at the most unfortunate moment.

This design solves the issue: it fits inbetween the Prusa I3 Rework slider and the carriage, and allows you to adjust the distance to the endstop easily.

Requires 2 or 3 M3 bolts and nuts.