Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/Social/Sources/SLRequest+Promise.swift

@@ -0,0 +1,37 @@
+#if !PMKCocoaPods
+import PMKFoundation
+import PromiseKit
+#endif
+import Social
+
+/**
+ To import the `SLRequest` category:
+
+    use_frameworks!
+    pod "PromiseKit/Social"
+
+ And then in your sources:
+
+    import PromiseKit
+*/
+extension SLRequest {
+    /**
+     Performs the request asynchronously.
+
+     - Returns: A promise that fulfills with the response.
+     - SeeAlso: `URLDataPromise`
+    */
+    public func perform() -> Promise<(data: Data, response: HTTPURLResponse)> {
+        return Promise { seal in
+            perform { data, rsp, error in
+                if let data = data, let rsp = rsp {
+                    seal.fulfill((data, rsp))
+                } else if let error = error {
+                    seal.reject(error)
+                } else {
+                    seal.reject(PMKError.invalidCallingConvention)
+                }
+            }
+        }
+    }
+}