Updated to work with 0.13

 - This is _totally_ experimental, and I haven't done exhaustive
   tests
 - 88 unit tests do pass though, and I added a new import test.
 - 0.12 and 0.13 seem to structure stuff a bit differently,
   probably due to changes in the FreeCAD lib wrappers.
 - Not tested on windows (but should work) or 0.12. Need some
   help there.