relax SVN archive

Fix for bmrb_read(). The object is called 'star.relaxation', not 'star.relaxation_data'.

Changes to generic_fns.relax_data.bmrb_read() for an abstracted bmrblib API.

This part of the API doesn't exist yet.

Fixes for the incorrectly named object 'star' (should have been 'self'!)

Removed the NMR-STAR version arg to the data specific bmrb_write() methods.

More fixes for the base class __init__() calling, and removed the placement of datanode into self.

Removed the initialisation of the non-existent v3.0 relaxation saveframes.

Fixes for the calls to the base class __init__() methods.

Clean up of the relaxation data bmrb_write() method.

The abstracted bmrblib API is now being called for all relaxation data.

Each Relaxation_v3_* class calls the base class __init__() method.

Wrote add() methods for the Relaxation_v3_1 and Relaxation_v3_2 classes.

This defined a stable API abstracting the saveframe structure from the user of bmrblib.