Toolchanger CoreXY

See it in action: [Cheap 3D Printed Toolchanger](https://www.youtube.com/watch?v=tlMmmSFyGIo)

This is rebuild of the Solidoodle 3 with CoreXY Kinematics and a toolchanger based loosely on the E3D toolchanger. Should be easy to adapt the toolchanger to other printers. With the toolchanger, it shrinks the printable area from 200x200x200 to about 196x150x210. Without the toolchanger, it goes to about 196x205x210. This mod improves speed considerably without adding updated hardware - I'm even using damaged stepper motors!

If you are only interested in the toolchanger, the rod spacing is a standard 45mm (like the Prusa), so it should transfer well to other printers. Originally used a 28byj, but updated to use a servo. Both still work, but the servo is easier. The stepper should last longer. If anyone is looking for mod ideas, an endstop would mean the stepper doesn't need to home or anything. Just run it until it stalls.

# Parts
- 4 3mm rods, salvaged from DVD/CD players
- 5 [