Including cython/c/h files in manifest

[yosefm]

Hi all.

during the conversion of SfePy to skbuild, I found that in order to get a working sdist, I needed to manually include in MANIFEST.in all pyx, c and h files that are needed during the build. I wonder if there is an automatic way to do it, perhaps using cmake, that I missed (just using cmake_with_sdist=True run the entire build but doesn't help the manifest). If I missed it I'd love to know. Otherwise, is there some best-practice for doing this?