MK2B Heat Bed mount for Monoprice Select Mini (MPSM)

https://youtu.be/aPAuHSU1c0g

UPDATE - 1/23/2019@1215: V12 - Improved tolerances of reinforcement bracket to avoid damage when inserting rods.

UPDATE - 1/19/2019@0122: V11 - Added bracket for outside edges to use the stock bed rails as reinforcements, as the previous version(s) will sag and bend under pressure from the bed.

UPDATE - 1/4/2019@1345: V10 - Moved and reinforced belt guides, replaced belt loop post with an empty hole for mounting an M3 screw with a nut. Bed screw spacing adju