2D Delta Drawbot

This is a set of files to make the 3D printed parts of a 2D "delta" kinematic drawbot.

It will need a few extras:
* most bolts are M3, you'll need a selection of bolts and some nuts with some grubscrews in the same size
* "shoulder" bolts are M8
* small bearings for elbows and wrists (4x for each elbow) with 3mm centres
* large skateboard bearings for the shoulder joints (4x in total) with 8mm centres
* timing belt (T2.5 I think)
* NEMA17 (or 14?) stepper motors
* stepper controller bo