treemap: minimum size

[rejetto]

Thank you very much for your work!
In the treemap, I'd like to set a minimum size (width and height) for boxes, so that if I have 2 values, like 10 and 1million, I'd still get a usable box for the 10.
Of course this will affect the adherence of the visualization to the data, but in return I'd get a clickable box.