Sankey, with different end note link treatment

Playing with the data from the wonderful Floweaver: https://github.com/ricklupton/floweaver/tree/master/docs/cookbook

https://floweaver.readthedocs.io/en/latest/

forked from tomshanley's block: Sankey with circular links

forked from tomshanley's block: Sankey, with different end note link treatment