pandas.core.groupby.SeriesGroupBy.hist doesn't take kwargs
I'd like to pass certain kwargs to the hist function of a SeriesGroupBy object (alpha, legend, etc). The plot function provides more kwargs (e.g. legend, but not alpha) but no **kwargs to forward to matplotlib. The documentation (viewed with ? in ipython) suggests that there should be a kwds argument, but in reality this is not the case.
