The sub-revision number is now also extracted and stored.
Added the v2.1 _Molecular_mass tag.
Changed the molecular weight variable name.
The entity saveframe has been significantly expanded and v2.1 is now supported.
The revision number is no longer set to 0 if it doesn't exist.
Better print out of the NMR-STAR version number.
Missing import.
The NMR-STAR version singleton now does all of the version number processing.
The v2.1 sf_framecode is now being pulled out of the tag category title.
Shifted the version singleton into its own module to allow it to be imported.
