relax SVN archive

Converted User_functions into a observer design pattern.

This will be used to notify the GUI that a user function has completed.

Added the structure user function menu to the spin viewer window.

Fix for the structure.load_spins user function window.

The 'combine_model' arg should have been 'combine_models'.

Another fix for _build_doc() for the handling of fn._doc_additional.

Fix for _build_doc() which was broken in the last commit.

_build_doc() now handles the fn._doc_additional structure for adding additional sections.

Removed the starting and ending newlines from the id_string_doc used as a tooltip in spin_id_element().

Only the description part of id_string_doc and not the title in spin_id_element().

All of the spin, residue, and molecule user functions now use _build_doc().

The spin ID string documentation object id_string_doc is now a list of the title and desc.