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 fi