Resolve pending Lintian issues

This package draw me attention because of its misleading short description which still mentioned bitshuffle filter. I took some time to resolve this and other pending minor issues with the packaging.

Something I also considered changing is making hdf5-filter-plugin recommend bitshuffle. It was previously included by the package, and now users must install bitshuffle by hand. However, this seems awkward to do so now, because bitshuffle ships both filter shared libraries and Python-specific binaries, which makes it also depend on Python tooling.

That can be resolved by creating a bitshuffle binary package that ships only the plugin shared objects (which provides hdf5-plugin-bshuf-{serial,openmpi}), and another that ships Python-specific binaries to work with NumPy. In order to avoid manual installation of filter packages, a general metapackage could install all plugins available in Debian. This could be an extension to specific metapackages suggested by @enrico. Let me know if that makes sense.

I've tagged this as a NMU, since I'm not from the Freexian Team, but I questioned myself if that maintainer line is updated. I noticed that package has been moved to Debian Science in Salsa (b601603c). I can rewrite the last commit to be a Team Upload if Debian Science is the actual maintainer team (even though I'm not myself formally in the team), or drop it entirely if that works better.