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

include/beast/http/impl/message_parser.ipp

@@ -26,8 +26,7 @@ message_parser<isRequest, Body, Fields>::
 message_parser(header_parser<
     isRequest, Fields>&& parser, Args&&... args)
     : base_type(std::move(static_cast<basic_parser<
-        isRequest, false, header_parser<
-            isRequest, Fields>>&>(parser)))
+        isRequest, header_parser<isRequest, Fields>>&>(parser)))
     , m_(parser.release(), std::forward<Args>(args)...)
 {
 }