High-performance mode via direct decoding for USB

This script uses direct decoding or passthrough of MJPEG or H264 streams from UVC camera into re-encoded stream provided over web-interface.

tools/usb_camera.sh -help
tools/usb_camera.sh -camera-format=MJPEG ...

Currently the H264 is consider rather broken:

tools/usb_camera.sh -camera-format=H264 ...