Clarify docstring: Series.sort_index() creates new instance (rather than sorting in-place)
all pandas objects return new objects except for indexing operators. the fact that Series.sort is actually in place is a historical fact and will be deprecated (in favor of a new method .sorted soon)

so this is superfluous 
 Thanks for the clarification (and the super-quick response!), and apologies for the noise. I just saw that this is indeed mentioned in the docs (for reference: http://pandas.pydata.org/pandas-docs/stable/basics.html#copying). It's good to know that `Series.sort()` will be deprecated soon. I think it is the fact that this method does an in-place modification (but most/all others don't) which has led to quite a bit of confusion amongst some colleagues of mine. Glad to hear that it will be consistent soon.
 this has been a wart for a while and I am going to fix it soon
it comes from the fact that np.sort is in place (for efficiency but odd for semantics)
