Size reductions for LibVrnaXXX

The improvements aren't phenomenal, but with a simple RLE applied to the memory initializer, I obtained:

LibVrna185 from 2.6Mb -> 1.1Mb
LibVrna211 from 1.5Mb -> 1.4Mb

Also, I renamed fold_constrained() to foldWithConstraint(), which looks more in sync with the naming policies of the scripting interface in general, and I implemented it in v1.8.5 as well.