relax SVN archive

Updated the module docstring.

Shifted the data.relax_xml.read() fn to Relax_data_store.xml_read().

Shifted create_str_elem() to PipeContainer.xml_create_str_elem().

Fixes for the Element.__repr__() method.

Shifted the create_diff_elem() fn to the DiffTensorData class.

Renamed a number of variables and methods.

Converted the create_hybrid_elem() fn to the PipeContainer.xml_hybrid_elem() method.

Fixes to the PipeContainer.xml_write() method.

Shifted the contents of create_top_level() into Relax_data_store.xml_write().

Shifted most of the PipeContainer.xml_write() method to the Relax_data_store.xml_write() method.