added delete_removed config param to deploy

README.md

@@ -22,6 +22,8 @@ deploy:
   concurrency: <number of connections> // Optional
   region: <region>  // Optional, see https://github.com/LearnBoost/knox#region
   headers: <headers in JSON format> // pass any headers to S3, usefull for metadata cache setting of Hexo assets
+  prefix: <prefix> // Optional, prefix ending in /
+  delete_removed: <true|false> // if true will delete removed files from S3. Default: true
 ```
 #### Example: header Cache-Control