This is awesome and I was just about to request for something like this too. Great job!
What is not awesome is that DMD spits out map files with invalid code points. :( DMapTreeMap>rdmd treemapgen.d test13_2056.map out.json std.utf.UTFException@std\utf.d(637): Invalid UTF-8 sequence (at index 15342) I've checked it with an editor and there are tons of invalid code points in the map file.
