Refactor HTTP serialization and parsing (API Change):

fix #404

Parsing and serialization interfaces have been fine tuned and unified.

For parsing these stream operations are defined:

* read
* read_header
* read_some
* async_read
* async_read_header
* async_read_some

For serialization these stream operations are defined:

* write
* write_header
* write_some
* async_write
* async_write_header
* async_write_some

examples/http_example.cpp

@@ -15,7 +15,7 @@
 int main()
 {
     // Normal boost::asio setup
-    std::string const host = "boost.org";
+    std::string const host = "www.example.com";
     boost::asio::io_service ios;
     boost::asio::ip::tcp::resolver r{ios};
     boost::asio::ip::tcp::socket sock{ios};
@@ -37,5 +37,5 @@ int main()
     beast::flat_buffer b;
     beast::http::response<beast::http::dynamic_body> res;
     beast::http::read(sock, b, res);
-    std::cout << res;
+    std::cout << res << std::endl;
 }