code: function concat(divider, sourcePath, relativePaths, done) {
    var writeDivider = false;
    each(relativePaths, function(relativePath, next) {
      var absoluteSourcePath = path.resolve(sourcePath, relativePath);
      var readStream = fs.createReadStream(absoluteSourcePath);
      if (writeDivider) process.stdout.write(divider);
      writeDivider = true;
      readStream.on('close', next).on('error', next).pipe(process.stdout);
    }, done);
  }
docs: Concatenate files from the source path into the standard output.
  @param {string} divider
  @param {string} sourcePath
  @param {Array.<string>} relativePaths
  @param {function(Error)=} done