Update .gitignore to avoid commit the unnecessary file of Mac, Xcode, Pods.
Add Podfile to manager the dependencies of libraries.

- Using AFNetWorking to manager the download http.
Add some customized log tools to log uniquely in mode DEBUG.
Add AsyncImage's core to download asynchronously an image and display it in an image view.

The QCAsyncImageManager handles the download the images in a queue (NSOperationQueue) to avoid having many request at the same time. We can change the max concurrency number dynamically.
 
Each download policy is described by priority, url cache policy, expected download directory and an tag name. We can control (cancel or resume) the request by tag name.

When the download is finished, the manager will notify to all the associated imageView to update.
Add the project Example to test the AsyncImage core.
Update structure of workspace.
Update .gitignore to avoid commit the file unnecessary files of workspace Xcode.