Hotend mounted Piezo Sensor Z-Probe (Alpha)

This is one of the early versions of what is now a mature product with over 200+ units in the wild. Feel free to use this in any way helpful (which complies with the CCA license) but if you want the best probing please see

https://www.thingiverse.com/thing:2319993

Update 16-7-17 latest thinking on firmware setup can be read here http://forums.reprap.org/read.php?1,767998,page=9

Description (Update History is below)

Following on from the excellent work done by Leadinglights and Mori