'zero': Constant zero baseline, i.e. a simple stacked plot.
'sym': Symmetric around zero and is sometimes called
‘ThemeRiver’.
'wiggle': Minimizes the sum of the squared slopes.
'weighted_wiggle': Does the same but weights to account for
size of each layer. It is also called ‘Streamgraph’-layout. More
details can be found at http://leebyron.com/streamgraph/.
labels:Length N sequence of strings
Labels to assign to each data series.
colors:Length N sequence of colors
A list or tuple of colors. These will be cycled through and used to
colour the stacked areas.