relax SVN archive

Updated the relax data store from_xml() method for support of the loading of the XML state file.

Docstring clarification of the dir arg.

Absorbed the load_xml() function into load_state().

After shifting the data store check to load_state() for all formats, the function only had one
statement.

Added a warning to the state.save() user function about the pickle format compatibility.

Added the pickle arg to state.save().

This allows the relax state - the contents of the relax data store - to either be saved as XML or as
a pickled object.

Created the relax data store is_empty() method.

Updates to the load_xml() function. This now does something!

Removed trailing whitespace.

Shifted the results.write() force arg to the end.

Bool args should be last!

The relax data store to_xml() method now can add all data pipes to the XML file (or a subset).

The results.write() method now asks to_xml() for just the current pipe to be stored, whereas
state.save() supplies no 'pipes' argument to have all pipes stored.