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/interest.hpp b/src/interest.hpp
index ea007bd..c433ae8 100644
--- a/src/interest.hpp
+++ b/src/interest.hpp
@@ -16,6 +16,7 @@
 #define NDN_INTEREST_HPP
 
 #include "common.hpp"
+
 #include "name.hpp"
 #include "selectors.hpp"
 #include "interest-filter.hpp"
@@ -28,7 +29,7 @@
 const time::seconds DEFAULT_INTEREST_LIFETIME = time::seconds(4);
 
 /**
- * An Interest holds a Name and other fields for an interest.
+ * An Interest holds a Name and other fields for an Interest
  */
 class Interest : public enable_shared_from_this<Interest>
 {