BodyReader and BodyWriter names are swapped (API Change):

Body::reader and Body::writer meanings are reversed, for
consistency with the names of the stream operations:

* Body::reader is used for read, read_some, async_read, async_read_some
* Body::writer is used for write, write_some, async_write, async_write_some

Actions Required:

* Swap the reader and writer names for user defined Body types
* Swap use of is_body_reader and is_body_writer

test/beast/http/span_body.cpp

@@ -34,7 +34,7 @@ struct span_body_test
             BEAST_EXPECT(req.body().size() == 3);
             BEAST_EXPECT(B::size(req.body()) == 3);
 
-            B::reader r{req};
+            B::writer r{req};
             error_code ec;
             r.init(ec);
             BEAST_EXPECTS(! ec, ec.message());
@@ -50,7 +50,7 @@ struct span_body_test
             using B = span_body<char>;
             request<B> req;
             req.body() = span<char>{buf, sizeof(buf)};
-            B::writer w{req};
+            B::reader w{req};
             error_code ec;
             w.init(boost::none, ec);
             BEAST_EXPECTS(! ec, ec.message());