code: function fill(fillWith, len){
      var buffer = new Buffer(len);
      buffer.fill(fillWith);
      return buffer.toString();
  }
docs: Create a new string filled with the supplied character
  @param {string} - the fill character
  @param {number} - the length of the output string
  @returns {string}
  @example
  ```js
  > s.fill("a", 10)
  'aaaaaaaaaa'
  > s.fill("ab", 10)
  'aaaaaaaaaa'
  ```
  @alias module:string-tools.fill