霍夫曼编码，功能为读取对应文件里的字符串源码，进行霍夫曼编码，输出码表字典和编码结果，编码效率等参数，最后提供解码-Huffman coding function to read the corresponding file in the source string, Huffman encoding, dictionary and code table output coded result, the coding efficiency and other parameters, and finally provide decoded