relax SVN archive

Modified the model-free default_value() and return_data_name() methods.

The heteronucleus type is now stored in 'spin.heteronuc_type'. The proton type has also been added,
and is located in 'spin.proton_type'.

Added some missing imports of physical constants.

Updated the epydoc compilation of the API docs to include all unit tests.

Removed a duplicated entry in __all__.

Updated the test_suite.unit_tests package __init__ module.

A package docstring was added, and the __all__ list completed.

Updated the test_suite.system_tests package __init__ module.

A package docstring was added, and the __all__ list completed.

Updated the test_suite package __init__ module.

A package docstring was added, and the __all__ list completed.

Removed all the subdirectories of test_suite and model_free from the API docs.

Fixed indentation in the Unit_test_runner.__init__ docstring to allow the API docs to be compiled.

All packages in the specific_fns and test_suite directories are now being included in the API docs.