Tidy up read_size_helper and dynamic buffers

fix #376

include/beast/http/impl/async_read.ipp

@@ -15,6 +15,7 @@
 #include <beast/core/bind_handler.hpp>
 #include <beast/core/handler_ptr.hpp>
 #include <beast/core/type_traits.hpp>
+#include <beast/core/detail/read_size_helper.hpp>
 #include <boost/asio/handler_alloc_hook.hpp>
 #include <boost/asio/handler_continuation_hook.hpp>
 #include <boost/asio/handler_invoke_hook.hpp>
@@ -160,6 +161,7 @@ operator()(error_code ec,
         case 2:
         case 3:
         {
+            using beast::detail::read_size_helper;
             auto const size =
                 read_size_helper(d.db, 65536);
             BOOST_ASSERT(size > 0);

include/beast/http/impl/read.ipp

@@ -15,6 +15,7 @@
 #include <beast/core/bind_handler.hpp>
 #include <beast/core/handler_ptr.hpp>
 #include <beast/core/type_traits.hpp>
+#include <beast/core/detail/read_size_helper.hpp>
 #include <boost/asio/handler_alloc_hook.hpp>
 #include <boost/asio/handler_continuation_hook.hpp>
 #include <boost/asio/handler_invoke_hook.hpp>
@@ -53,6 +54,7 @@ read_some_buffer(
     do_read:
         boost::optional<typename
             DynamicBuffer::mutable_buffers_type> mb;
+        using beast::detail::read_size_helper;
         auto const size =
             read_size_helper(buffer, 65536);
         BOOST_ASSERT(size > 0);