Request: Playback message suppression

[Valinwolf]

I would like to see the "Buffer Playback..." and "Playback complete." messages hidden. I couldn't find a setting for it in ZNC, so I'm requesting it in this plugin. I just realized that's because this plugin is the cause of the message... Can we get a setting to disable this? Actually I may fork and create a pull request... seems simple enough. Done. Submitting a PR.