tokenizer cleanup: cut down on overloading

not necessary now that we have Scala and default arguments
don't hardcode dependency of TokenLexer on TokenMapper
fooling around with tokenizer stuff

attempting progress towards not having Tortoise depend on any
back end or engine stuff
simplify TokenMapperInterface using Option
relocate some tests to parse package

since they have a runtime dependency on prim classes, they aren't
purely lex-only