http://iosdevelopertips.com/user-interface/creating-circular-and-infinite-uiscrollviews.html
https://github.com/darcyliu/SampleCode/tree/master/StreetScroller
http://code4app.com/ios/UIScrollview%E6%97%A0%E9%99%90%E5%BE%AA%E7%8E%AF/51e74b826803faad28000000
http://code4app.com/ios/%E5%BE%AA%E7%8E%AF%E6%BB%9A%E5%8A%A8%E8%A7%86%E5%9B%BE/5052e6a26803fa4a0c000003
https://developer.apple.com/library/ios/samplecode/StreetScroller/Listings/StreetScroller_InfiniteScrollView_m.html#//apple_ref/doc/uid/DTS40011102-StreetScroller_InfiniteScrollView_m-DontLinkElementID_5
https://github.com/rs/SDWebImage
fastimageCache
