Monoprice Select Mini V2 Modular Toolhead and Carriage

This modification greatly improves the Monoprice Select Mini V2's fuctionality by replacing the toolhead/carriage with a modular system consisting of a modified X-carriage and swappable toolheads.

See the full documentation on Hackaday:
https://hackaday.io/project/182956-monoprice-select-mini-v2-modular-toolhead

Special thanks to Kadah for the excellent CAD model of the MPSM V2. This model helped ensure that the design's dimensions would work with the printer, while minimizing the need for trial and error.
Kadah's model can be found here: https://www.thingiverse.com/thing:2681912

Update20211208_1405: Step file for M3 captive nuts added, as requested

Happy printing!