hdf5doc

Description:
    Added note that unlimited dimensions require chunking.
        -- Closes Bugzilla entry 1489.
    Removed '-1' value accompanying H5S_UNLIMITED; such values, assigned 
        by the library to a constant, should not be considered public as 
        they may change without notice.
    Added "Last modified" tag and "See Also" section.
    Edited for clarity, other minor edits, updated HTML coding.
Tested:  Firefox