src: Refactoring common.hpp and minimizing exposed includes

Face class has relatively large rewrite to hide internals using
Implementor pattern.  As of this commit, <boost/asio.hpp> is not
automatically included whenever ndn-cxx/face.hpp is included.  If it is
needed to directly work with io_service, asio.hpp should be specifically
included.

Change-Id: Ie742b851025b4e3da634eb981319df0f42937855
diff --git a/src/encoding/encoding-buffer.hpp b/src/encoding/encoding-buffer.hpp
index 07ee33d..0464287 100644
--- a/src/encoding/encoding-buffer.hpp
+++ b/src/encoding/encoding-buffer.hpp
@@ -13,17 +13,14 @@
  * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
  */
 
-#ifndef NDN_ENCODING_BUFFER_HPP
-#define NDN_ENCODING_BUFFER_HPP
+#ifndef NDN_ENCODING_ENCODING_BUFFER_HPP
+#define NDN_ENCODING_ENCODING_BUFFER_HPP
 
 #include "../common.hpp"
 
 #include "buffer.hpp"
-#include "tlv.hpp"
 #include "block.hpp"
 
-#include <boost/lexical_cast.hpp>
-
 namespace ndn {
 
 namespace encoding {
@@ -566,4 +563,4 @@
 
 } // ndn
 
-#endif // NDN_ENCODING_BUFFER_HPP
+#endif // NDN_ENCODING_ENCODING_BUFFER_HPP