Allow users to specify a class for each way

This adds the ability to mark ways with a user-defined
class in the profile. This class information will be included
in the response as property of the RouteStep object.

src/extractor/scripting_environment_lua.cpp

@@ -342,6 +342,10 @@ void Sol2ScriptingEnvironment::InitContext(LuaScriptingContext &context)
         &ExtractionWay::weight,
         "road_classification",
         &ExtractionWay::road_classification,
+        "forward_classes",
+        &ExtractionWay::forward_classes,
+        "backward_classes",
+        &ExtractionWay::backward_classes,
         "forward_mode",
         sol::property([](const ExtractionWay &way) { return way.forward_travel_mode; },
                       [](ExtractionWay &way, TravelMode mode) { way.forward_travel_mode = mode; }),