Allow duplicate advertisement packets during scan

[andySigler]

Thanks for the great library! I am building an application that would greatly benefit from the ability to pick up duplicate advertising packets from a peripheral while scanning. I have read that on iOS this can be specified. Sorry if this feature already exists, I have not been able to find any documentation of it.

[randdusing]

Should have this finished shortly, but I'm kind of confused. I'm not exactly sure what CBCentralManagerScanOptionAllowDuplicatesKey does. If I set it to No, I still get multiple scan results from devices. If I set it to Yes, I get multiple scan results from devices, but seemingly a lot more.