Supporting new HDF5 data types

[aragilar]

There's a discussion/RFC on adding new data types at https://forum.hdfgroup.org/t/hdf5-rfc-adding-support-for-16-bit-floating-point-and-complex-number-datatypes-to-hdf5/11975

I think the alternate floating point types are fine, given we try to find what we can load, and load the best one, though that logic hasn't been applied to complex types yet.

For the complex types, we likely need to work out the migration path (it'd be nice to handle this at the HDF5 level, but I suspect that won't happen), and similarly with booleans.

Any other thoughts?