Added support for hdf5 format in Storage class.
Added a first example for handling hdf5 files.
Added a small tutorial for handling HDF5 files in manual
Actually exit() when no pytables is installed. Name of sample a bit more meaningful.
Moved sections of HDF5 and BLZ from tutorials to data_sources chapter
Merge branch 'hdf5_docs' of github.com:FrancescAlted/blaze into hdf5_docs
Rephrasing the requirement message
Merge pull request #135 from FrancescAlted/hdf5_docs

HDF5 DataDescriptor docs and examples