DiamondActivityIndicator 介绍
DiamondActivityIndicator 是 UIActivityIndicatorView 类的改进版本，基于一个来自 @Sentry_NC
的概念开发 (请看: http://dribbble.com/shots/1185018-Diamond-Loading-Indicator-GIF).
DiamondActivityIndicator 官网
https://github.com/thomasfinch/Diamond-Activity-Indicator-for-iOS