This allows stream_cb backends to implement blocking
behavior inside read_fn, and still get notified when the user
wants to cancel and stop playback.
Signed-off-by: Aman Gupta <aman@tmm1.net>
The license text refers a "above copyright notice", so I guess it'd be
good to actually provide such a notice.
Add the license to some files that were missing it (since in theory, our
Copyright file says that such files are LGPL by default).
Remove the questionable remarks about the license in the client API.
