Feature request: support the DD property of the SGF standard

[Trevoke]

Hi!

The SGF standard has a markup property, DD, for dimming areas of the board.
This one's probably a pain to support because, if I understand correctly, the markup stays until it's removed - https://www.red-bean.com/sgf/properties.html#DD: ( DD[] clears any setting, i.e. it undims everything.).

Still, would be great to have a client who supports the entire SGF range of markup tools!