relax SVN archive

Expansion of the chemical shift anisotropy saveframe.

Added a catch for Rex error values of None.

All the relaxation data saveframes now contain all the equivalent data as in general relaxation.

Entity IDs are going into the model-free saveframe and missing parameter errors are now handled.

Removed a test for duplicated data - data can be duplicated!!!

An entity IDs fix for the general relaxation saveframe reading.

Molecule names are converted to entity IDs and vice versa for BMRB writing and reading.

Entity ID numbers are now supported throughout the relaxation data and model-free saveframes.

The translate function now handles numpy arrays.

Created the structure.get_pos() user function for extracting atomic positions.