REM Operator (For BASIC Comments)

Implementing the REM operator (single quote) turned out to be simpler than anticipated.  The REM operator type of REM always occurs at the end of a line, therefore, it can be treated as the end of the line except that the REM operator token (with comment string) will be added to the end of the RPN output list.

A new REM operator token handler was implemented, which first checks if the command stack is not empty or if the current token mode is not command (occurs for assignment statements without the LET keyword).  Otherwise the REM operator being processed occurred at the beginning of the line and no current command needs to be processed.

To process the current command, the end of line token handler is called since it contains all the needed functionality for processing the command when the end of a line is reached.  A new end of line token is created and passed to the end of line token handler.  A new token was needed in case the command changes the end of line token into another token to add to the RPN output list (as the INPUT command does).  If the command does not use this token, the end of line token handler will delete it.  If an error is returned, then the end of line token is deleted and the error is returned.  Otherwise, the REM operator token is appended to the end of the RPN output list.

Since the REM operator token acts as the end of the line, the table entry for the REM operator code entry was changed to include the end expression and end statement flags.  The pointer to the new REM operator token handler was also added.  Several new REM tests were added to translator test #15 for the REM operator on various types of commands.  Some error tests were also added.

[commit da69b3ba07]