Added ability to request broadcast packages

[pBauma]

Wraped the function call, so it can be used with setTimeout()

[pBauma]

I also added the corresponding pull request to the arduino client of the library.

[VaclavSynacek]

Hello @pBauma Thank you for this pull request. I am really pleased any time I see people using and contributing to this lib.

However I do not understand the intent of this change. What is the broadcast really doing and why it cannot be done as simple request for a value?

My other concern is with the MQTT topic path chosen. I usually run more things on the same central MQTT broker so IMHO it is safer for all RF24SN values stay in RF24SN/* topic path. This way RF24SN does not accidentally interfere with MQTT topics of other applications talking to the same MQTT broker.

[pBauma]

Thanks for your reply @VaclavSynacek With the broadcast package it is possible to send information to all nodes at once. At the moment you would have to send the same information to all nodes individually with RF24SN/out/x/y.

I am using it to broadcast the time to all nodes so I don't have to use a Realtime clock.

That's a good point it would indeed better to move it to RF24SN/broadcast/.