Return a list of stops for a particular route.
        
        Arguments:
            `rt`: route designator
            `dir`: route direction (INBOUND, OUTBOUND)
        
        Response:
            `stop`: (stop container) contains list of 
                `stpid`: unique ID number for bus stop
                `stpnm`: stop name (what shows up on the display in the bus,
                         e.g., "Forbes and Murray")
                `lat`, `lng`: location of stop
                
        http://realtime.portauthority.org/bustime/apidoc/v1/main.jsp?section=stops.jsp

def stops(self, rt, direction):
        """
        Return a list of stops for a particular route.
        
        Arguments:
            `rt`: route designator
            `dir`: route direction (INBOUND, OUTBOUND)
        
        Response:
            `stop`: (stop container) contains list of 
                `stpid`: unique ID number for bus stop
                `stpnm`: stop name (what shows up on the display in the bus,
                         e.g., "Forbes and Murray")
                `lat`, `lng`: location of stop
                
        http://realtime.portauthority.org/bustime/apidoc/v1/main.jsp?section=stops.jsp        
        """
        url = self.endpoint('STOPS', dict(rt=rt, dir=direction))
        return self.response(url)