encoding: Extending Block and EncodingBuffer interfaces

Now it is possible to use constructors to create Block from
EncodingBuffer and EncodingBuffer from Block.

Block->EncodingBuffer conversion is potentially dangerous and should be
used only in exceptional cases, such as Data packet encoding: to encode
the signed part first and then extend signed part with signature and
other related fields.

Change-Id: I5a13bf0c196ecd0d45dfa14c4cb6f4a9f612420c
diff --git a/src/encoding/block.hpp b/src/encoding/block.hpp
index a2f19be..895df49 100644
--- a/src/encoding/block.hpp
+++ b/src/encoding/block.hpp
@@ -39,6 +39,12 @@
   Block();
 
   /**
+   * @brief Create block based on EncodingBuffer object
+   */
+  explicit
+  Block(const EncodingBuffer& buffer);
+  
+  /**
    * @brief A helper version of a constructor to create Block from the raw buffer (type and value-length parsing)
    */
   Block(const ConstBufferPtr &buffer);