Implement Functions as a service.

[ikeough]

Functions should behave the same from one language to the next. Similar to how we've proposed building the geometry service, we could have a functions service that provides the validated function implementations that can be called from any language implementation.

This would supersede #23 and #31.

[ikeough]

I'm not going to do this. As it's not clear that functions are going to survive the "modernization" of IFC, it doesn't make sense to put a lot of effort into this. If functions are required, I recommend that we make per-language implementations.