New(ish) plugin: logstash-input-mqtt

Hi!

I created a basic input plugin https://github.com/widarlein/logstash-input-mqtt, for mqtt which actually has gotten some traction, even though I just created it for my own purposes. It is poorly documented, but it is simple enough to understand. My original intention was to publish it as a proper plugin, but I have neither had the time or motivation to properly finish the docs or to maintain it. To top it all off, I'm not even a ruby developer.

I got an [offer](https://github.com/widarlein/logstash-input-mqtt/issues/1#issuecomment-196322067) from @ph to move it to the logstash-plugins repo, which I would love. It would be nice if it could be helpful to other people :)

Is this still a possibility? Can I handover the plugin in its entirety to you guys? This has been nagging at my conscience, but better late than never, I guess.

I see that there has been some forks made that has among other things updated versions and dependencies and someone pushed it to rubygems. I'm not sure how to handle this practically?