brief Demo code to calculate moments

实现了交互式的抠图，用户只需要用红线标记前景，绿线标记背景，就能将前景抠出来，实现了lazysnapping这篇文献中的方法-To realize the interactive matting, users need only in red mark the foreground. The green background markers, can the foreground to pull out, the realization of the method lazysnapping th