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/tlv-security.hpp b/src/encoding/tlv-security.hpp
index 8e1f224..ab10201 100644
--- a/src/encoding/tlv-security.hpp
+++ b/src/encoding/tlv-security.hpp
@@ -10,8 +10,8 @@
  * ndn-cxx library copyright, permissions, and redistribution restrictions.
  */
 
-#ifndef NDN_TLV_SECURITY_HPP
-#define NDN_TLV_SECURITY_HPP
+#ifndef NDN_ENCODING_TLV_SECURITY_HPP
+#define NDN_ENCODING_TLV_SECURITY_HPP
 
 #include "tlv.hpp"
 
@@ -29,4 +29,4 @@
 } // namespace tlv
 } // namespace ndn
 
-#endif // NDN_TLV_SECURITY_HPP
+#endif // NDN_ENCODING_TLV_SECURITY_HPP