add streamGetbpm to Stream.hs

[jarmitage]

bpm <- Link.getTempo ss is already available here, so it would be nice to add streamGetbpm here:

Tidal/src/Sound/Tidal/Stream.hs

Lines 754 to 759 in bc03ed8

	streamGetcps :: Stream -> IO Double
	streamGetcps s = do
	let config = sConfig s
	ss <- Link.createAndCaptureAppSessionState (sLink s)
	bpm <- Link.getTempo ss
	return $! coerce $ bpm / (cBeatsPerCycle config) / 60

[jarmitage]

getbpm :: Stream -> IO Double
getbpm s = fmap (\cps -> cps * 2 * 120) (streamGetcps s)

[matthewkaney]

As of #1059 this has been added, and then #1083 closes the loop by adding getbpm and setbpm.