Shaded line plots

[EDIT 10/2022: the link is dead] ~~https://github.com/jbusecke/xarrayutils/blob/master/doc/plotting.ipynb~~

I think hvplot is able to do this with area, but need to manually calculate the min + max first. Would be nice to have something similar to the notebook `shaded_line_plot(da2, 'member',spread_style='quantile', spreads=[0.5,1], alphas=[0.3, 0.4], color='C1');`