Enhancement: indicate water with thick border only

[almccon]

Suggestion from twitter: https://twitter.com/mjray/status/1100002976813457409

the "toner" maps would be much more useful for coastal areas IMO if seas were a thick black line around the edge, rather than a solid black toner-eater

That's actually a really good idea. It would need to be a third style variant (in addition to the existing toner and toner-lite variants that we currently have). Maybe we call it toner-white or toner-whitewater?

We don't have any current roadmap for when we might make improvements to the Toner style, but I'm recording this suggestion as an issue here just because it's a cool idea, and it would be nice if we could include it.

Also, if any other contributors in the open source world wanted to start working on this style variant, there's nothing stopping them. (It just might be a while before we could deploy it on Stamen servers)