code: function(str, num, padding) {
      var half, front, back;
      num   = coercePositiveInteger(num);
      half  = max(0, num - str.length) / 2;
      front = floor(half);
      back  = ceil(half);
      return padString(front, padding) + str + padString(back, padding);
    }
docs: *
  @method pad(num, [padding] = ' ')
  @returns String
  @short Pads the string out with [padding] to be exactly `num` characters.
  
  @example
  
  'wasabi'.pad(8)      -> ' wasabi '
  'wasabi'.pad(8, '-') -> '-wasabi-'
  
  @param {number} num
  @param {string} [padding]
  
  *