说明：  用简单神经网络(ANN)实现的手写数字识别(minst),可直接运行，用的是Tensorflow框架，通过该例程可以掌握Tensorflow基本用法
(With a simple neural network (CNN) to achieve the handwritten numeral recognition (minst), can be run directly, using the Tensorflow framework, through the routine can master Tensorflow basic usage)