RTMP library upgrade

[ericxtang]

We currently use the joy4 RTMP library. It's an incompletely implementation of the RTMP standard, and we should move to a better lib. For example, if you use OBS on a mac, you can see LPMS works with x264 encoder, but breaks with Apple VT H264 encoder.

There is currently no good RTMP libraries in golang, so we'd probably have to do integrate something like nginx-rtmp