registry: update meerk40t entry (v1.2.0, 3d category) (#389)

* registry: meerk40t v1.2.0, move to design category

* registry: meerk40t to 3d category (CAM/G-code neighbours)

* readme: add Fabrication & Machine Control category

* copy: describe only released 1.2.0 capabilities

* registry: meerk40t v1.3.0 with released hardware-control commands