任意动态下拉刷新Refresh效果

任意动态下拉刷新Refresh效果，源码KYRefreshControl，这份下拉刷新代码包含一个抽象类KYRefreshControl，令开发者轻松实现任意动画和效果的下拉刷新。Demo中有一个KYRefreshControl的子类，仅重写了init方法，便做出来了一个像笔写字一样的下拉刷新效果。 A bare bone implementation of a pull to refresh. You can easily create your own style pull to refresh with this class, compatible with UIRefreshControl api. This is also a demo of reimplementation of David Rönnqvist’s blogpost-codesample-PullToRefresh by subclassing KYRefreshControl.