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/core/ostream.cpp

@@ -10,10 +10,9 @@
 
 #include <beast/core/streambuf.hpp>
 #include <beast/unit_test/suite.hpp>
+#include <boost/lexical_cast.hpp>
 #include <ostream>
 
-#include <beast/core/to_string.hpp>
-
 namespace beast {
 
 class ostream_test : public beast::unit_test::suite
@@ -23,7 +22,8 @@ public:
     {
         streambuf sb;
         ostream(sb) << "Hello, world!\n";
-        BEAST_EXPECT(to_string(sb.data()) == "Hello, world!\n");
+        BEAST_EXPECT(boost::lexical_cast<std::string>(
+            buffers(sb.data())) == "Hello, world!\n");
     }
 };