add a MyParser type with Tables as user state
get TypeChecker into Parser
build typechecking into expression parser
change type error to an 'unexpected' error
clean up expressionP typechecker
make a base parser in terms of expression parser
pull in old expression tests with untyped parser
refacter typechecker into submodules for different AST componenets
fix array indexing tests
remove unnecessary 'Syntax' directory
clean up typecheck, rename to typecheckexpression
start statement typechecking tests
add assignment type checker and tests
add a basic for test