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.

unit_tests/engine/guidance_assembly.cpp

@@ -53,7 +53,8 @@ BOOST_AUTO_TEST_CASE(trim_short_segments)
                                       0},
                                      0,
                                      3,
-                                     {intersection1}},
+                                     {intersection1},
+                                     {}},
                                     {324,
                                      "Central Park West",
                                      "",
@@ -74,7 +75,8 @@ BOOST_AUTO_TEST_CASE(trim_short_segments)
                                       0},
                                      2,
                                      3,
-                                     {intersection2}}};
+                                     {intersection2},
+                                     {}}};
 
     LegGeometry geometry;
     geometry.locations = {{FloatLongitude{-73.981492}, FloatLatitude{40.768258}},