单词频率统计，遍历目录，统计 txt , cpp , h , cs 类型文件中的单词频率，并可用命令行参数-e2，-e3来选择连续的两个或三个单词频率统计，排序输出。-Word frequency statistics, traverse directories, statistics txt , cpp , h , cs file type in the word frequency, and the available command line parameters-e2,-e3