Add the option to choose the size of a marker in the map.

[hugomvlopes]

Like we choose the color, the icon etc... of a marker should be very interesting having the option to set the size of our marker. So it would be possible to create different kind of relevance in the markers and a better organization. It would be cool too if exist an circle with custom image option.

Thanks for all your job!

[mnalis]

• related: https://github.com/umap-project/umap/issues/859