py-pynio: new package (#10074)

* py-pynio: new package

* Major re-working to add some of the optional dependencies, and make it conform to the approach described in the pynio setup.py comments. Much of it turned out to be too complicated, and I have added some notes in comments to explain this to future adventurers.

* Added variants for the hdf5 and gdal dependencies, which do seem to be genuinely optional. Also added absolute dependencies for jpeg and zlib, which setup.py says it wants, but were being found as the os-installed versions.

* Added descriptions for the new variants, and moved them to above the dependencies