Spring-loaded NEMA 17 steppers / belt tensioner

This is an improvement to precisely set and keep a given belt tension by pulling the stepper motor downwards with a spring.

Some people were asking for it in the original design, mainly to reduce the risk of over-tightening the belt.

So here it is: obviously you'll need an appropriate spring and a fews more nuts & washers.

Additionally, it might even compensate belt length variations during print if the stepper is kept slightly loose

Update: I've added a 4-screw version, probably req