Most of the pipe_control.structure.main.assemble_coordinates() function has been shifted into the
assemble_coord_array() function of the new lib.structure.internal.coordinates module. The
pipe_control function now only checks the arguments and assembles the structural objects from the
relax data store, and then calls assemble_coord_array() to do all of the work.
This code abstraction increases the usefulness of the atomic coordinate assembly and allows it to be
significantly expanded in the future, for example by being able to take sequence alignments into
consideration.
