Added option to notify discoveries immediately

This option disables the buffering of broadcast data. Setting this
option will let noble emit a 'discover' event for each broadcast on
linux, instead of only emitting the event for every second broadcast
received.

The BLE sensors we use are only sending a broadcast every other minute, so we don't really want to miss every other reading.

I'm not to fond of the implementation, but this was the only way I could think of that wouldn't break backwards-compability.

I'm more than happy to refactor/rewrite it.