code: function (dstPath, group, options) {
          _.defaults(options || (options = {}), DEFAULT_OPTIONS);
          var separator = options.separator;
          var heads = options.heads;
          var extnames = options.extnames;
          var images = [];
          fsys.walk(dstPath, function(prefix, dir, file, stats) {
              for (var i = 0; i < heads.length; i++) {
                  for (var j = 0; j < extnames.length; j++) {
                      var reg = new RegExp('^' + heads[i] + separator + group + separator +'.+\\' + extnames[j] + '$');
                      if (file.match(reg)) {
                          images.push(path.join(dir, file));
                      }
                  }
              }
          });
  
          return images;
      }
docs: getImages
  @param {String} dstPath
  @param {String} group
  @param {Object} options
  @returns {Array} images is files path
  @example
  var dstPath = './test/image/sprite';
  var group = 'logo';
  var options = {
  separator: '-',
  };
  var out = getImages(dstPath, group, options);
  console.log(out);
  > [ './test/image/sprite/sprite-logo-hoge.png', './test/image/sprite/sprite-logo-fuga.png',,,etc ]