7.0 1012 2018
1. Cluster function support.
2. Add iotsdk for device manager.
3. Change cloud keepalive from json to binrary.
4. Change server thread num cache from 50 to 200.
5. add api to get ws user count.
6. add api to get webrtc user count.
7. Pre record support, default is disable, and default length is 15s.