hdf5doc

Description:
    Create separate explanations for contiguous, unfiltered chunked, 
        and filtered chunked datasets.
    Add "Caveat:" that H5Dget_storage_size does not differentiate 
        between 0 (zero), the value returned for the storage size 
        of a dataset with no stored values, and 0 (zero), the value 
        returned to indicate an error.
    Additional minor edits, and HTML and template updates.
Tested:  Firefox