Make EasyData a direct submodule of CMDimData.
Also conform to changes in HDF5 API:
- HDF5.exists -> Base.haskey
- g_create -> create_group
- g_open -> open_group
- attrs -> attributes
- d_write -> write_dataset
- d_read -> read_dataset
- a_write -> write_attribute
- a_read -> read_attribute
- HDF5.HDF5Group -> HDF5.Group
- HDF5.HDF5Dataset -> HDF5.Dataset
- HDF5.HDF5File -> HDF5.File