Better CMake targets

[igfraga]

It would be nice to have nice CMake targets like lib3mf::cppbindings. The recommended way to integrate with CMake (https://lib3mf.readthedocs.io/en/master/source/Cpp/LandingPage.html) is not great because it uses a global variable CMAKE_CURRENT_BINDING_DIR (which looks like an official cmake thing but I don't think it is).

On a general note, I'd love libraries to just define their targets and not touch the global environment at all, but it's an uphill battle in this dystopic cmake world we live in.

[waebbl]

As far as I can see, there's only one target which could be exported, the library lib3mf::lib3mf. The different bindings are just header interfaces which all need to use the library. But I agree, it would be more comfortable if there were config and target cmake files exported during build, not only a pkg-config file. This could also ease finding of correct header files by consumers of this library.

[vijaiaeroastro]

The refactoring done in PR #346 addressed this issue and introduces the lib3mf::lib3mf as a target to link to.