New buffers() replaces to_string() (API Change):

A new function, buffers(), returns an implementation defined object
which wraps a ConstBufferSequence and supports formatting to a
std::ostream.

The function to_string is removed, as the new implementation allows
conversion to string using boost::lexical_cast on the return value
of the call to buffers(). Streaming to an output stream is more
efficient: no dynamic allocations are performed.

Example:

    streambuf sb;
    std::cout << buffers(sb.data()) << std::endl;

test/http/write.cpp

@@ -14,7 +14,6 @@
 #include <beast/http/write.hpp>
 #include <beast/core/error.hpp>
 #include <beast/core/streambuf.hpp>
-#include <beast/core/to_string.hpp>
 #include <beast/test/fail_stream.hpp>
 #include <beast/test/string_ostream.hpp>
 #include <beast/test/yield_to.hpp>