New ostream() returns dynamic buffer output stream (API Change):

This eliminates beast::write output for dynamic buffers and replaces
it with the function ostream() that wraps a caller provided dynamic
buffer and returns the result as a std::ostream derived object.
Callers may now produce formatted output into any object meeting the
requirements of DynamicBuffer using operator<< and the standard stream
modifiers such as std::endl.

This new technique is more efficient, as implementations of operator<<
can now write directly into the output using std::ostream::write and
std::ostream::put.

Example of use:

  beast::streambuf sb;
  beast::ostream(sb) << "Hello, world!" << std::endl;

include/beast/core/impl/streambuf.ipp

@@ -9,7 +9,6 @@
 #define BEAST_IMPL_STREAMBUF_IPP
 
 #include <beast/core/detail/type_traits.hpp>
-#include <beast/core/detail/write_dynabuf.hpp>
 #include <boost/assert.hpp>
 #include <algorithm>
 #include <exception>
@@ -871,14 +870,6 @@ read_size_helper(basic_streambuf<
     return (std::min)(max_size, low);
 }
 
-template<class Alloc, class T>
-basic_streambuf<Alloc>&
-operator<<(basic_streambuf<Alloc>& streambuf, T const& t)
-{
-    detail::write_dynabuf(streambuf, t);
-    return streambuf;
-}
-
 } // beast
 
 #endif