Hey, I was bored - again.
I've added a new feature, rectangular filling for tilesets.
Use it by holding Ctrl.
The marker will resize according to the mouse position. You can select multiple tiles to use a pattern. Simply click to place the tiles, as usual.
I intentionally added this to quickly clear zones, but then I realized that you could quickly create patterns with this, too.
There are some issues with this + undo, I'll fix that, I guess.
By the way, I also improved the performance of Flood Fill.