Move library include to the top

This helps ensure that library inclusion is self sustainable

example/asymmetric/chaining.cpp

@@ -4,6 +4,8 @@
 //    (See accompanying file LICENSE_1_0.txt or copy at
 //          http://www.boost.org/LICENSE_1_0.txt)
 
+#include <boost/coroutine/all.hpp>
+
 #include <iostream>
 #include <iomanip>
 #include <string>
@@ -11,7 +13,6 @@
 #include <sstream>
 
 #include <boost/bind.hpp>
-#include <boost/coroutine/all.hpp>
 #include <boost/foreach.hpp>
 
 typedef boost::coroutines::asymmetric_coroutine<std::string> coro_t;