Removed unimplemented CharDiet tests -- there's no need for them, we'll just implement the rest of the CharSet tests instead.
Improve performance of the fslex-compatible backend for large DFAs making extensive use of Unicode (e.g., the F# compiler's lexer) by using a HashMap instead of a regular map. The keys are chars, so the HashMap has performance close to an IntMap, and importantly, avoids the rebalancing overhead of the standard Map.