wheel content is stored in platlib subfolder #48

Investigate why hdf5plugin is stored in hdf5plugin-2.0.0.data/platlib/.
Check whether this is normal or not.
This is due to setting root_is_pure in the subclass of bdist_wheel that tweaks the wheel generation to make one wheel working for the different versions of python.

Initially raised here: https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!topic/h5py/EMLVilY8oHk