Properly emit multipart/form-data in post endpoint

Fixes #9.

Author: gaul

src/main/java/org/gaul/httpbin/HttpBinHandler.java

@@ -371,7 +371,9 @@ baos, new Deflater(Deflater.DEFAULT_COMPRESSION,
                         data.put(part.getName(), new String(baos.toByteArray(),
                                 StandardCharsets.UTF_8));
                     }
-                    response.put("data", data);
+                    response.put("data", "");
+                    response.put("form", data);
+                    response.put("json", JSONObject.NULL);
                 } else {
                     ByteArrayOutputStream baos = new ByteArrayOutputStream();
                     Utils.copy(is, baos);