Feature proposal: pandas vectorize decorator
`numpy` has a very useful `vectorize` decorator: http://docs.scipy.org/doc/numpy/reference/generated/numpy.vectorize.html that allows writing a function for scalars and then pass in arrays transparently. Under the hood, the function is called multiple times on subsets of the data.

I'm currently writing code that operates on a `Series` object. Some of those functions can also be passed in DataFrames and still work the same while some would require special logic. I think a pandas vectorize decorator could be very useful for these cases. In my specific case, I can just write that myself easily but I thought I'd bring it up. Perhaps this already exists and I just don't know about it.  
