STG1 (yet another custom printer!)

I've been printing for a couple of years now, and much like a young Jedi aspiring to become a master, I felt it was time to try to make my own printer.

I had a few goals for this project:

- large print area with a relatively small footprint.
- direct drive extruder (no corexy)
- avoid rods and linear bearings where possible (z only)
- use v slot for x and y (because i wanted to play with v slot)
- use 2040 extrusion for stability.
- recycle as much of my folgertech 2020 i3 as possible

The inspiration was the FT-5, along with some of the projects I collected in my 'i3 rework' collection here -- thanks to all of those people! Even if I didn't use a part directly, they helped shape the direction I was going to go with things.

Based on the FT-5, the things I changed the most were:
- no melamine!
- z motors connect directly to the rods, no belts to tighten
- x/y use v slot gantries rather than slides.
- the x bar sits on top of the printer -- the cube doesn't exte