Building models from b-rep building blocks

[hannobraun]

Right now, models are limited to whatever can be specified using the data structures in fj. Under the hood, those data structures are then converted into boundary representation (b-rep) structures, which are the basis for any further processing in the CAD kernel.

While still should always be the preferred workflow where possible, models should be able to generate those b-rep structures directly, as a fallback. Providing this functionality would make Fornjot much more powerful. It would also be very error-prone to use though. For this reason, it would probably be marked as "experimental" indefinitely (see #46).

The way b-rep structures are represented and defined is undergoing some changes right now (see #242, for example), and I expect many more changes to happen in the near future. While this issue is not blocked, strictly speaking, it might be best to let it simmer for a bit, until the APIs for defining b-rep structures have matured a bit.

[hannobraun]

As I mentioned in the original issue description, this isn't really ready to be worked on. I've added an entry to the feature wishlist. Closing.