Modified the PredictiveSets record so it uses nonterminal and terminal indices; the functions still (temporarily) operate over the original nonterminal/terminal types, but we'll wait to optimize them until later.
Removed a type parameter from PrecedenceSettings which is no longer needed.
Adapted the code in LR.fs to work with the new TaggedGrammar implementation.
Brought Lr0.fs and Slr1.fs back into the project and _mostly_ finished adapting them to use TaggedGrammar.
NOTE : This commit does not compile -- there are a few small errors which haven't been fixed yet.