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 board - my code is designed to use the Eggbot EiBotBoard
* 6mm carbon rod, around 1m total for each arm but this depends on how big you want the machine
* pen lift servo is a standard micro servo

Pulleys on the stepper motors are taken directly from droftarts' excellent pulley library, the arm pulleys are modified from the library so I've marked this whole thing as a remix.