encoding: Construct Block from istream

Change-Id: Iee330e861197e9c347fd7c15a887c2b9fc5552be
diff --git a/include/ndn-cpp-dev/encoding/block.hpp b/include/ndn-cpp-dev/encoding/block.hpp
index 85cdaf5..de8c5a5 100644
--- a/include/ndn-cpp-dev/encoding/block.hpp
+++ b/include/ndn-cpp-dev/encoding/block.hpp
@@ -50,6 +50,11 @@
   Block(const uint8_t *buffer, size_t maxlength);
 
   Block(const void *buffer, size_t maxlength);
+
+  /*
+   * @brief A helper version of a constructor to create Block from the stream. 
+   */
+  Block(std::istream& is);
   
   /**
    * @brief Create Block from the wire buffer (no parsing)