Reinforced minimal MK8 w/ soft-PLA printing spur

A re-re-re-work of the minimalist MK8 replacement. The originals I printed suffered after several km of filament from "arm fatigue" (see gallery, orange PLA) which gradually reduced the applied filament pressure... bad for lots of things, but most esp. fast printing.

Although this basic design has evolved nicely (e.g., http://www.thingiverse.com/thing:53125)... and those other works largely solve it, this design also solves a problem with printing the soft/flexible PLA filaments... herniation