code: function createMd5Path(oldpath, md5, separator, expand, opt) {
      var ext = path.extname(oldpath);
      var basename = path.basename(oldpath, ext);
      if(expand) ext = separator + expand + ext;
      if(md5) {
          //如果指定了md5合的的方式，则使用配置的函数来处理
          if(opt && typeof opt.md5 == 'function') {
              ext = opt.md5(ext, md5);
          }
          else {
              ext = separator + md5 + ext;
          }        
      }
      return path.join(path.dirname(oldpath), basename + ext).replace(/\\/g,'/');
  }
docs: 据md5生成路径