Previously, it was a publically accessible but invalid value (valueEmpty).
* Deprecate internal use of UndefinedValue(), NullValue(), FalseValue(), TrueValue()
* Guard against Empty, Result, Reference values from escaping the package
* Streamline what we get from "otto/parser"
* Get rid of some "otto/parser" cruft
* FunctionExpression => FunctionLiteral
* The debugger statement (debugger) should do nothing (not panic)
* Fix aspects of function expression call evaluation