Suggestion: implement Q-Q plots
I see that there was some discussion of this years ago (PR #1501), but was wondering if there are any plans of implementing these in the future.

One thought would be to have `qqplot` be a `Series` method which optionally takes another `Series` as an argument.  If this argument is missing then `qqplot` could fall back on the quantiles from some theoretical distribution (default Gaussian, say), perhaps imported from `statsmodels`.  Even without `statsmodels` integration a purely empirical method could be quite useful for providing a very fast way of comparing two distributions.