Show tooltip when hovering node

[nikolay-borzov]

Useful when node is too small to fit caption

[evmar]

Good idea! Might be as simple as adding a title attribute on the DOM node.

[nikolay-borzov]

I believe the first version has it.
But It would be great to provide a hook method where a user can attach custom behaviour to node element (e.g. add multiline tooltip)

[evmar]

I guess it would go somewhere around here:

https://github.com/evmar/webtreemap/blob/master/src/treemap.ts#L115

I experimented with letting the user provide a function here, I can't remember why I removed it.