Add doApplyChanges (ATAC) and getSleepMode (ATSM)

You'll need to apply changes after changing the data rate, or baudrate.
Correct text in (commented out) diag and disable diag in setSleepPin
Do the "apply changes" in config() after doing setDataRate

Maybe we should do the "apply changes" in setDataRate.
Reduce default timeout of receiveData to 500

This influences sendDataAndWaitForReply because that function uses
receiveData with its default timeout. Not sure if this is a good thing.
Bugfix, waitForAck should only accept the ack from a specific source

Also, the implementation of waitForAck was wrong anyway, but incidentally
it was always giving an OK for a received packet.
Add a Python implementation of the XRF library, plus a "hub" example