Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/CoreBluetooth/Sources/CBCentralManager+Promise.swift

@@ -0,0 +1,29 @@
+import CoreBluetooth
+#if !PMKCocoaPods
+import PromiseKit
+#endif
+
+
+private class CentralManager: CBCentralManager, CBCentralManagerDelegate {
+  var retainCycle: CentralManager?
+  let (promise, fulfill) = Guarantee<CBCentralManager>.pending()
+
+  @objc func centralManagerDidUpdateState(_ manager: CBCentralManager) {
+    if manager.state != .unknown {
+      fulfill(manager)
+    }
+  }
+}
+
+extension CBCentralManager {
+  /// A promise that fulfills when the state of CoreBluetooth changes
+    public class func state(options: [String: Any]? = [CBCentralManagerOptionShowPowerAlertKey: false]) -> Guarantee<CBCentralManager> {
+    let manager = CentralManager(delegate: nil, queue: nil, options: options)
+    manager.delegate = manager
+    manager.retainCycle = manager
+    manager.promise.done { _ in
+      manager.retainCycle = nil
+    }
+    return manager.promise
+  }
+}