relax SVN archive

Improvements for the relaxation data storage tag categories.

Different NMR-STAR dictionary definitions are supported and the tag names are now located in the
tag name dictionary.

Added v3.1 support for the T2.

Full implementation of v3.1 NMR-STAR support.

T2's are still missing, causing an import error.

Redesign for different NMR-STAR dictionary version support.

All class variables have been converted into dictionaries created upon instantiation.

Some class name changes.

Started to implement different NMR-STAR version support.

There are obvious design issues here, preventing this from working!

Changed some imports in preparation for support for different NMR-STAR versions.

Code rearrangement.

The BMRB read(), write(), and display() methods called by the user functions has been shifted to
generic_fns. This allows bmrblib to be purely a package providing an API for the NMR-STAR
dictionaries, with reading and writing done by pystarlib.

Shifted the tag name prefix creation code into bmrblib.tag_category.TagCategory.

Created the heteronucl_NOEs and heteronucl_T2_relaxation saveframes.