HDF5: Implement saving to HDF5-Ph-Data.

See:
https://github.com/tritemio/FRETBursts/wiki/HDF5-smFRET-format---Draft-0.2-(WIP)
HDF5: Implement loading from HDF5-Ph-Data (no multi-spot)
HDF5: Implement loading from HDF5-Ph-Data for multi-spot.
HDF5: fix names and descriptions for detector polarization
HDF5: rename number_confocal_spots -> num_spots
HDF5: fields reanamings and add more ALEX info
HDF5: Use hdf5() for the new format and hdf5_legacy() for the old-one.
HDF5: fix typo in metadata
Fix installation via "python setup.py install"
Docs: update example data files URL in notebooks
Merge branch 'hdf5_smfret'