Add FreeCAD files.

Dependencies

• [2] 5GR5Z2VC Add MH3SS2 footprint library.
• [3] G45Y4KYS Add KiCAD files.
• [4] T3DMCYVW Add README

Change contents

• file move: mh3ss2.pretty (----------) → mh3ss2.pretty (d--r------)
  [1.0]

  [2.16]
• file addition: mech (d--r------)
  [1.0]
• file addition: switch.FCStd (----------)
  [0.23]
• file addition: plate.FCStd (----------)
  [0.23]
• file addition: layout.FCStd (----------)
  [0.23]
• file addition: exp.FCStd (----------)
  [0.23]
• file addition: central_pcb.FCStd (----------)
  [0.23]
• file addition: cap.FCStd (----------)
  [0.23]
• file addition: board.FCStd (----------)
  [0.23]
• file addition: assembly.FCStd (----------)
  [0.23]