Add support for manufacturerSpecificData (Android) and kCBAdvDataManufacturerData (iOS)

[etwilliams]

I've been looking into the library for use in my companies BLE apps. It seems very simple to use and I look forward to being able to add this to our toolkit. One feature we use a lot is embedding information into the advertising data. Is it possible to add ScanRecord.manufacturerSpecificData (for Android) and kCBAdvDataManufacturerData (for iOS) into the BluetoothPeripheral class? I'm an Android developer and could help with that side.

[Reedyuk]

Nice idea, happy for you to put in a PR for this.