GitLab

This major commit prepares v2 of lib3mf
- adds the Automatic Component toolkit
  - this removes the COM interface
  - autogenerates language bindings for multiple languages
- reworks the way in which properties are handled
- implementes multiproperties and compositematerials
- adds basic (and automatic) documentation using sphinx / https://readthedocs.org/
- improves/changes lib3mf in multiple other minor ways
- ... but has several open issues left