Merge pull request #128 from Itheum/develop

Extra Assets Support

README.md

@@ -239,15 +239,12 @@ Items below marked "required" are the "minimum" required for it to be compatible
 ```json
 {
   "description": "Data NFT description", // required
+  "data_preview_url": "https://previewdata.com",
   "attributes": [
     {
       "trait_type": "Creator", // required
       "value": "creator address"
     },
-    {
-      "trait_type": "Data Preview URL", // required
-      "value": "https://previewdata.com"
-    },
     {
       "trait_type": "extra trait",
       "value": "extra trait value"