Changes

* 16 '''String expression too complex''' - A string expression need to be broken down into smaller expressions.* 17 '''CannotCONTinue''' - CONT can only be used if program was stopped by [ESC] or a STOP in program - not after END.* 18 '''Unknown user function''' - A DEF FN must be executed before calling an FN function.* 19 '''RESUMEmissing:''' - End of program has been reached while in error processing mode. Use ON ERROR before RESUME.* 20 '''UnexpectedRESUME''' - RESUME is only used in error processing mode, ON ERROR GOTO statement must be used first.