Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Sources/hang.m

@@ -0,0 +1,29 @@
+#import "AnyPromise.h"
+#import "AnyPromise+Private.h"
+@import CoreFoundation.CFRunLoop;
+
+/**
+ Suspends the active thread waiting on the provided promise.
+
+ @return The value of the provided promise once resolved. 
+ */
+id PMKHang(AnyPromise *promise) {
+    if (promise.pending) {
+        static CFRunLoopSourceContext context;
+
+        CFRunLoopRef runLoop = CFRunLoopGetCurrent();
+        CFRunLoopSourceRef runLoopSource = CFRunLoopSourceCreate(NULL, 0, &context);
+        CFRunLoopAddSource(runLoop, runLoopSource, kCFRunLoopDefaultMode);
+
+        promise.ensure(^{
+            CFRunLoopStop(runLoop);
+        });
+        while (promise.pending) {
+            CFRunLoopRun();
+        }
+        CFRunLoopRemoveSource(runLoop, runLoopSource, kCFRunLoopDefaultMode);
+        CFRelease(runLoopSource);
+    }
+
+    return promise.value;
+}