Black box: older recordings read as before, single vehicles told apart, each platform end its own tolerance

- A light pattern asked for in a recording made before the lamps were
  written is checked as the signal it shows, as before.
- Whether the couplings were written is told by the format (the
  movement in the cab samples), not by there being any: a recording
  where every train is a single vehicle has none, and the user going
  over to another vehicle left the timetable shown.
- The 2 m a train may stand off the platform is at each end, not for
  both together.

StarterNG.Tests/BlackBox/PlatformTests.cs

@@ -47,6 +47,15 @@ public class PlatformTests
         Assert.Equal(1, stop.OffPlatform, 1);
     }
 
+    [Fact]
+    public void Each_end_has_its_own_tolerance()
+    {
+        // the head 1.5 m past the stop point, the tail 1.5 m past the platform's end
+        var stop = Stop(-1.5f, 204f, 201);
+        Assert.True(stop.OnPlatform);
+        Assert.Equal(3, stop.OffPlatform, 1);
+    }
+
     [Fact]
     public void A_train_within_the_platform_is_along_it()
     {