*
@method repeat([num] = 0)
@returns String
@short Returns the string repeated [num] times.
@example

'jumpy'.repeat(2) -> 'jumpyjumpy'
'a'.repeat(5)     -> 'aaaaa'
'a'.repeat(0)     -> ''

*
function(num) {
      var result = '', str = this;
      if(!isNumber(num) || num < 1) return '';
      while (num) {
        if (num & 1) {
          result += str;
        }
        if (num >>= 1) {
          str += str;
        }
      }
      return result;
    }