Rtmpdump default

I beleave most people use this as easy to use replacment of rtmpsrv. So I changed default output mode to rtmpdump.

If you don't agree just don't accept this pull request.

btw: this pull request is dependent on https://github.com/andreafabrizi/rtmpSnoop/pull/11 so if you going to accept this please accept this as second one.