Don't pass by const-value for a read-only view.

I can't see a reason we pass by const-value here.

Note: changes API because of the `route_parameters` header.

include/osrm/route_parameters.hpp

@@ -79,7 +79,7 @@ struct RouteParameters
 
     void addCoordinate(const boost::fusion::vector<double, double> &received_coordinates);
 
-    void getCoordinatesFromGeometry(const std::string geometry_string);
+    void getCoordinatesFromGeometry(const std::string &geometry_string);
 
     short zoom_level;
     bool print_instructions;