GRBL for Chinese CNC3040-like machines. WIP.

04 May 2020: First release
18 Apr 2020: Manual Tool change and start of tool table implemented
06 Apr 2020: Support of g54-59 offsets
- Display gcode parser state
  - Working coordinate display on main 3D window
  - Coordinate touch off and tool probing
  - Error display similar to LinuxCNC
28 Mar 2020: Basic Sender program available
- move to grblHal as the grbl driver for its more comprehensive gcode support
18 Mar 2020: Migration to STM32CubeIDE
05 Mar 2020: A and B axis basic functionality added
- Add option to manualy home each axis (similar to LinuxCNC)
04 Mar 2020: Complete PCB editing of dongle.
02 Mar 2020: Fix some initial bugs related to using 8bit vars for 16bit ports.
01 Mar 2020: Reorder pin assignments.

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