* added support for Paper servers.
* added optional configuration for controlling the plugin's mechanics.
* should now cooperate better with other plugins that also manage item frame visibility.
WARNING: Due to a Spigot bug (also affects Paper) entities allowed to go through a portal linked to another portal int he same world will be lost. If you disable strictLinking in the config, you will probably want to enable the acls to prevent entities from using "same world" portals.