WIP: First attempt to approach the issue bob.bio.base#106

1. Created mechanism to save dict in to hdf5
2. Created mechanism to get a dict out of hdf5
3. [black] the hdf5 test cases (sorry for the long diff in this one)
4. [sphinx] Documented the functions I created

This is related to bob.bio.base#106 (closed)

ping @andre.anjos @amohammadi