Support for RunCam Device Protocol

More recent RunCam cameras such as Split or Micro Swift 3 come with serial connection and support RunCam Device serial protocol. Protocol allows controlling camera's parameters ("OSD via transmitter") and functions (i.e recording off/on) remotely via telemetry send from flight-controller.

More details can be found here https://github.com/betaflight/betaflight/wiki/RunCam-Device-Protocol