Machine Axis Exercise gcode

This gcode runs 100 loops of:

• home
• zig-zag across a 160x160mm square (at z=18mm)
• zig-zag across a 160x160mm circle
• cross-stitch around a 160x160mm square
• spiral out a 160mm spiral
• spiral in a 160mm spiral
  it will display progress om a LCD if you have one.

I wrote it to test my axis (should be safe on any bed of at least 160mm. It moves slowly, but I speed it up to 300% and let it go...