Series string  operators
Makes the string operators available to the `Series.str` object

``` python
In [1]: a = pd.Series(['%s', '%s'])

In [2]: a.str % 2
Out[2]: array(['2', '2'], dtype=object)

In [3]: a = pd.Series(['a', 'b'])

In [4]: a.str * 2
Out[4]: array(['aa', 'bb'], dtype=object)

In [5]: a.str + 'test'
Out[5]: array(['atest', 'btest'], dtype=object)
```

This already works on the series itself, eg 

```
In [22]: a = pd.Series(['a', 'b'])

In [23]: a * 2
Out[23]:
0    aa
1    bb
dtype: object
```

so why would you also want it on `s.str` ?
 Oh man, sorry.
 No problem!
