Function to tell if an adapter is already connected? #350

Feature Description

This might not be possible because of platform differences, but I would like a peripheral_connected() or similar function for Centrals, even if it just returns a bool and no info about the peripheral.

I see that Peripheral has is_connected(), but this isn't the same because Windows doesn't remember paired peripherals the way Linux does, and it always requires a scan. I would like to be able to avoid the scan by getting information about the currently connected device, if any.