Simplify color format routines slightly
Print out bInterfaceNumber in uvc_print_stream_ctrl
Don't call status_cb if it is NULL
CSupport multiple simultaneous streams from the same device.

A new uvc_stream* API is added, along with a uvc_stream_handle type to encapsulate the
state of a single UVC stream. Multiple streams can run alongside each other, provided
your USB connection has enough bandwidth. Streams can be individually stopped and
resumed; the old uvc_start/stop_streaming API is still provided as a convenient way
to interact with the usual one-stream devices.
Rudimentary support for MJPEG streams
Add a README
Add a changelog