lib: speed up exiting from async handler

Now we're using libusb_handle_events_timeout_completed()
instead of the deprecated libusb_handle_events_timeout(),
and notify our async state machine when rtlsdr_cancel_async()
is called. This speeds up exiting from any program that uses the
device asynchronously.

Signed-off-by: Steve Markgraf <steve@steve-m.de>
lib: add SVEON STV27, sort device list

Signed-off-by: Steve Markgraf <steve@steve-m.de>