This function has been coded to use the UCSF selection syntax as described in Gary Thompson's post
located at https://mail.gna.org/public/relax-devel/2007-01/msg00014.html (Message-id:
<f001463a0701071417w6bd7927cp8fdd052e698575ec@...>).
The function makes use of three new selection functions - tokenise, parse_token, and molecule_loop.
The first two are described at https://mail.gna.org/public/relax-devel/2007-01/msg00036.html
(Message-ID: <1168883717.7569.511.camel@...>). The last function is similar to the spin_loop
function described in the same post. All three are yet to be implemented (although stubs have been
created for the functions).
The RelaxError 'RelaxSpinSelectDisallowError' has been created to prevent spins from being selected
by the user function.
The unit tests for generic_fns.residue.delete() have been updated and two more added:
test_delete_all() and test_delete_shift().
