Prusa-style encoder knob for Ender 3

### UPDATE: ###
I haven't tried it yet, but it looks like bleeepy's remix is better. Please check it out:

https://www.thingiverse.com/thing:4593634

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VERSION 3

V3 is a total redesign, and should work a lot better. It's a good bit larger (sized up properly for the Ender 3), and I've replaced the fiddly encoder shaft slot with one especially-designed to fit the Ender perfectly -- there's a bar that fits into the slot at the tip of the E