hdf5_ep

C++ API improvement
Description:
    - Reorganized some exception classes to reflect the HDF5 object
      hierarchy and provide extendibility.
        DataSetIException -> LocationException -> Exception
        DataTypeIException -> LocationException -> Exception
        GroupIException -> LocationException -> Exception
        AttributeIException -> LocationException -> Exception
        FileIException -> GroupIException -> LocationException -> Exception
    - Added throwException() to these subclasses and use it in H5Location
        and H5Object member functions to throw an exception that is specific
        to the object that invokes the member function.  Applications that
        catch the base exception can continue to do the same.
    - Many cleanup for inconsistencies in comments/headers.
Platforms tested:
    Linux/64 (jelly)
    Linux/64 (platypus)
    Darwin (osx1010test)