Open Platform Geared B'Struder, tailored for Ender 3 mount

The purpose of this design is to provide a reliable and compact geared
bowden extruder, with a moderate gear ratio, open and accessible
mechanism, and a novel look while hopefully sticking true to the
aesthetic of the B'Struder. It is designed for mounting on the Ender 3
(or perhaps CR-10) in the same location as the original extruder. As a
bonus, the idler arm is on the opposite side from the Ender 3 original,
so that you can have a geared extruder without having to flash a
boot-loader a