BREAKING CHANGE: For users using this module with CLUSTERS the db schema has changed for retained messages. There is a migration available in migrations.js named from9to10 that can be used to move all db to the new format. Also, if you are passing a conn to options (that is using clusters) now you also have to set cluster : true in options. To make this change back compatibile and faster in non cluster envs that option is used in order to use a different set of operations that only works in cluster envs