Added defaults to Timeline and Response initializers to maintain backwards compatibility.

Source/Response.swift

@@ -47,7 +47,7 @@ public struct Response<Value, Error: ErrorType> {
         - parameter response: The server's response to the URL request.
         - parameter data:     The data returned by the server.
         - parameter result:   The result of response serialization.
-        - parameter timeline: The timeline of the complete lifecycle of the `Request`.
+        - parameter timeline: The timeline of the complete lifecycle of the `Request`. Defaults to `Timeline()`.
 
         - returns: the new `Response` instance.
     */
@@ -56,7 +56,7 @@ public struct Response<Value, Error: ErrorType> {
         response: NSHTTPURLResponse?,
         data: NSData?,
         result: Result<Value, Error>,
-        timeline: Timeline)
+        timeline: Timeline = Timeline())
     {
         self.request = request
         self.response = response

Source/Timeline.swift

@@ -51,18 +51,20 @@ public struct Timeline {
     /**
         Creates a new `Timeline` instance with the specified request times.
 
-        - parameter requestStartTime:           The time the request was initialized.
-        - parameter initialResponseTime:        The time the first bytes were received from or sent to the server.
-        - parameter requestCompletedTime:       The time when the request was completed.
-        - parameter serializationCompletedTime: The time when the response serialization was completed.
+        - parameter requestStartTime:           The time the request was initialized. Defaults to `0.0`.
+        - parameter initialResponseTime:        The time the first bytes were received from or sent to the server. 
+                                                Defaults to `0.0`.
+        - parameter requestCompletedTime:       The time when the request was completed. Defaults to `0.0`.
+        - parameter serializationCompletedTime: The time when the response serialization was completed. Defaults 
+                                                to `0.0`.
 
         - returns: The new `Timeline` instance.
     */
     public init(
-        requestStartTime: CFAbsoluteTime,
-        initialResponseTime: CFAbsoluteTime,
-        requestCompletedTime: CFAbsoluteTime,
-        serializationCompletedTime: CFAbsoluteTime)
+        requestStartTime: CFAbsoluteTime = 0.0,
+        initialResponseTime: CFAbsoluteTime = 0.0,
+        requestCompletedTime: CFAbsoluteTime = 0.0,
+        serializationCompletedTime: CFAbsoluteTime = 0.0)
     {
         self.requestStartTime = requestStartTime
         self.initialResponseTime = initialResponseTime