all: Adding typedefs near forward declarations of Interest/ContentObject/Name

refs #29
diff --git a/apps/ndn-app.h b/apps/ndn-app.h
index 749dc9e..57d1d83 100644
--- a/apps/ndn-app.h
+++ b/apps/ndn-app.h
@@ -34,6 +34,10 @@
 
 class Interest;
 class ContentObject;
+
+typedef Interest InterestHeader;
+typedef ContentObject ContentObjectHeader;
+
 class Face;
 
 /**