Switched from OCE 0.x to OCCT-7.3.x as CAD kernel

While OCE looked good at first sight, it turned out that the boolean algorithms are in bad shape. This is not surprising since OCE is based on OCC-6.9.x which is rather dated. The vanilla OCC is usable even without community patches.

• CSG operations are more robust and accurate
• the official binaries use static OCC and Freetype on all supported platforms

Polyhedrons and other multi-polygon shapes are supported.

v0.9.1

Update README.md

major issues resolved:

• transform finally works (differentiates between uniform and non-uniform scaling)
• extrusion fixed (crashed most of the time)

Support for Round-Edges added

• sharp edges can be converted to round-edges with a specified radius (fillets)
• error output improved (number conversion shows var names)
• CLI revised

v0.7: shape splitting support:

- shapes can be splitted into their faces:
- example: a cylinder disassembles into three faces
- triangulation is retained if requested (.stl output format)
  -> this means face stl files can be merged (useful for declaring subsets)

minor:
- cone shapes are supported

Binaries are compiled automatically via Travis-CI and AppVeyor

v0.6

Update occ-csg.cpp

fixed extrusion commands

extrusion of 2d files didn't work and is fixed now

2d primitive for CAGs including text support

• circles, polygons and circles can be created in addition to the 3d primitives
• text shapes are finally supported (ttf font file is required)

v0.3

Support for bounding boxes added:

• get bounds min and max
• get bounding box as geometry (important for csg)

BREP file support

We support the BREP file format since BREP files are significantly smaller than STEP files.