Simpson GUS construction based 3D printer

Variant of fully printed 3D printer based on [Simpson GUS concept](https://reprap.org/wiki/GUS_Simpson).

Printer was modified to be able to use squared heated bed and touch probe. As firmware was intended to be used [modified Marlin](https://sourceforge.net/projects/marlinpp) with standard Atmega2550 and Ramps 1.4 board (design to cost ;-)).

Construction was built and used for a while, but project was discontinued due to switch on cartesian CoreXY variant of printer later. However I was so impressed by this construction so I decided to put it here for someone who want to try to make it running ;-)

Here are some videos from quick tests of printer mechanics and modified Marlin FW:

* https://youtu.be/EC8Vc0Y3SwI
* https://youtu.be/KLIYvSXHRx8
* https://youtu.be/vAyoxbl9Me0
* https://youtu.be/RSLSo5djzvA
* https://youtu.be/uOudku6Uui4
* https://youtu.be/ESs8r99B3E4