实现霍夫曼编码和霍夫曼解码，并统计原文件中的各个字符出现的频率，将字符及其出现的频率保存至txt文件中，构建的霍夫曼树也将被保存至txt文件中。-Achieve Huffman coding and Huffman decoding and statistical frequency of each character in the original document that appears to save the characters and their frequency of occur