Add streambuf write():

This function performs serialization of a variable list of arguments
to a streambuf. It accepts a wide variety of argument types, using
boost::asio::buffer and boost::lexical_cast where possible.

include/beast/http/impl/basic_headers.ipp

@@ -8,7 +8,6 @@
 #ifndef BEAST_HTTP_IMPL_BASIC_HEADERS_IPP
 #define BEAST_HTTP_IMPL_BASIC_HEADERS_IPP
 
-#include <beast/http/detail/writes.hpp>
 #include <beast/type_check.hpp>
 
 namespace beast {