DOC: Add example of converting timedeltas to periods
Something like this is super useful and not clear (to me). Maybe there's a more idiomatic way? If so, I didn't see it in the docs.

http://stackoverflow.com/questions/18215317/extracting-days-from-a-numpy-timedelta64-value

(Possible enhancement, adding accessors to datetime-typed columns for things like `day`, `year`, etc. similar to `.str.` or `.cat.`)
