Consider publishing generated capnp and uhdm_types.h as release artifacts

[MikePopoloski]

As mentioned in #484 a potential way to use UHDM is to take only the capnp and uhdm_types.h files and write the databases yourself without needing the extra C++ wrapper layer that is generated. As part of a versioned release process it would be nice to publish these as outputs, and to consider reducing uhdm_types.h to the bare minimum enum definition (moving the other code out of it to somewhere else).

[hzeller]

First step: With recent change #488, the UHDM.capnp is part of the install and shows up in lib/uhdm (though maybe share/uhdm/UHDM.capnp might be another possible choice.

• $PREFIX/lib/uhdm/UHDM.capnp
• $PREFIX/include/uhdm/uhdm_types.h

Still todo:

• [ ] actually create regular releases that allow to download the build artifacts
• [ ] Reduce stuff in uhdm_types to just the enum