add Debug.AddPoint()

Shared/Debug.cs

@@ -90,6 +90,12 @@ namespace SemiColinGames {
       AddRect(rect, color);
     }
 
+    [System.Diagnostics.Conditional("DEBUG")]
+    public static void AddPoint(Point p, Color color) {
+      AddLine(p.X, p.Y - 2, p.X, p.Y + 1, color);
+      AddLine(p.X - 2, p.Y, p.X + 1, p.Y, color);
+    }
+
     [System.Diagnostics.Conditional("DEBUG")]
     public static void AddLine(Point start, Point end, Color color) {
       if (lineIdx >= MAX_LINE_VERTICES) {