Tags give the ability to mark specific points in history as being important
Last commit with algorithm in `trajectories.py` processing edges in date order
Last version with global sorting of edges to determine trajectories.
Last version aiming to use only the contours from `get_1_outerm` in `set_max_speed`.
Last commit choosing max-speed contour with radius4
Last revision writing invalid eddies
Last version targetting a single input SHPC in `eddy_graph`
Last version assuming date index is days since 1950-1-1
Last version where we want `inst_eddies` to only create shapefiles and not append to them.