* raise now creates a real exception
* New primitive (get-exception-message EXCEPTION) to get message from an exception
* use (raise "message") or (raise (list "Exception" "message"))
* Exception can be one of: "AssertionError", "Exception", "KeyboardInterrupt", "MacroError", "ParseError", "ReadError", "RunTimeError", "ScanError", or "UnhandledException"
* (raise ...) now has proper tracebacks