docs: function output(sourceCode, filePath) {
      return new Promise(function (resolve, reject) {
          mkdirp(path.dirname(filePath), function (ioErr) {
              if (ioErr) {
                  reject(ioErr);
                  throw ioErr;
              }
              fs.writeFile(filePath, sourceCode, function (writeErr) {
                  if (writeErr) {
                      reject(writeErr);
                      throw writeErr;
                  }
                  resolve();
              });
          });
      });
  }