relax SVN archive

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.

Created the T1 tag category.

Further object simplifications.

The __init__() methods have been shifted into the TagCategory base class in bmrblib.tag_category.

Code simplification by placement of many objects into the saveframe namespace.

Created the unused HeteronuclT1Software tag category class.

Created the HeteronuclT1Experiment tag category object.