Allow different methods of correlation when using corrwith
Hi,

The `corr` method for DataFrames is exceedingly useful, especially since one can specify methods other than the Pearson correlation.  I think it would be nice if this same argument were available when using `corrwith`.  Perhaps there is another workaround, but right now if one wants to calculate all the Spearman (say) correlations with a specific variable, it seems necessary to calculate the full Spearman correlation matrix and subset to the column you care about.

Thanks.