all: InterestHeader and ContentObjectHeader refactoring to Interest and ContentObject

refs #29
diff --git a/helper/ndn-header-helper.h b/helper/ndn-header-helper.h
index a5a4d2f..cce07dd 100644
--- a/helper/ndn-header-helper.h
+++ b/helper/ndn-header-helper.h
@@ -40,7 +40,7 @@
  *
  * Ndn doesn't really have a header, so we need this class to
  * determine type of Ndn packet and return corresponent header class,
- * InterestHeader or ContentObjectHeader
+ * Interest or ContentObject
  *
  * Throws UnknownHeaderException if header type couldn't be determined
  */