• Adds a new error code, SCPErrorBluetoothConnectionFailedBatteryLow, that is passed into the connectBluetoothReader completion handler when connection failed due to the reader's battery being critically low.
• Fixes Issue #124: Crash when Bluetooth reader reports low battery but BluetoothReaderDelegate was released.
• Fixes Issue #121: SCPReader isCharging and batteryLevel weren't being updated if the SCPBluetoothReaderDelegate didReportBatteryLevel: wasn't implemented.