code: function process (filePath, complete) {
          var filename = path.basename(filePath),
              pathParts = path.dirname(filePath).split(path.sep)
  
          // we'll get an empty arrary if we overslice
          pathParts = pathParts.slice(transform.by)
          pathParts.push(filename)
  
          var newPath = pathParts.join(path.sep),
              fileData = files[filePath]
  
          // don't need the old fileData anymore,
          // since we are re-adding with the new path
          delete files[filePath]
          files[newPath] = fileData
  
          complete()
        }
docs: transform the path