HDF5 V2.0

[bnlawrence]

There are some major changes with version 2.0, some basic defaults have changed, and there is native complex number support.

We need to ensure that all our 1.X tests are not polluted by upstream library changes (i.e either force them to write old format files or make sure we have data files), and we need to add 2.X tests, and see if our existing complex support is compatible with this advancement.

[valeriupredoi]

@bnlawrence good call! At the moment the conda-forge package build is struggling conda-forge/hdf5-feedstock#274 - they need to do several rebuilds for various components and then I guess they will have it out. I am not supporting an installation from PyPI - there are lots of things that can go boom with one, and we'd not know which ones are due to 2.x or just bad wheels. Once 2.x appears on conda-forge I will do the testing dance 🍺