EndOfInput is now a Terminal
Added Symbol.GetFollowSet without an implementation
NonTerminal now knows if it is the start symbol
Follow(NonTerminal) contains the EndOfInput if the non-terminal is the start symbol
Renamed IItemProducer to IProductionPart
Added IProductionPart.GetSymbolsTrailing
Added IProductionPart.GetAllSymbols
Added Production.IsEndingWith
Started to implement follow sets
A bit of cleanup
Refactored First/FollowSet production