relax SVN archive

Added 4 unit tests for the generic_fns.spin.delete() function.

Debugged the spin creation function.

Fixed another bug in the spin creation unit test.

Implemented the generic_fns.spin.create() function.

Fixed a bug in the unit test for spin creation.

Changed one of the spin creation unit tests to send the spin to a different molecule and residue.

Wrote 2 unit tests for the generic_fns.spin.create() function.

One tests that the function works correctly, the second that it fails correctly.

Split the 'test_copy_within_molecule_fail' unit test in two, for the 2 failures.

Added a new point in the data model redesign document - the new sequence user function class.

The idea is that this is a class that handles the whole of the molecule-residue-spin structure.

Removed the spin.read(), spin.sort(), and spin.write() user function from the redesign document.

These can be implemented in a single user function class which handles molecules, residues, and
spins together.