docs: function simpleMap(map, lvls, opts, type, ext, callback) {
      opts = utils.clone(opts);
      lvls--;
      if(lvls < 1) {
          opts.simple = false;
          opts.recursive = true;
          opts.type = type;
          opts.ext = ext;
      }
      var folders = map.__filter({type:'directory'}, true);
      var count = folders.length;
      var errs = [];
  
      function end(err) {
          if(err) {
              errs.push(err);
          }
          if(--count !== 0) {
              return;
          }
          if(errs.length) {
              callback(errs);
              return;
          }
          callback(null, map);
      }
      folders.forEach(function (folder) {
          folder.__map(opts, function (err, fMap) {
              if(err) {
                  end(err);
                  return;
              }
              if(lvls < 1) {
                  end();
              } else {
                  simpleMap(fMap, lvls, opts, type, ext, end);
              }
          });
      });
  }