You can now see what you're drawing before committing to it. This works
by passing the second_paint_event from the ImageEditor to the tool.
We also pass the active layer which makes it easier for the tool to
keep his logic in layer-relative coordinates even while drawing preview
states directly into the ImageEditor backing bitmap.
Tool mouse event handlers now receive both a layer-relative mouse event
and the original event. This is needed for the move tool since it moves
the layer and thereby changes the origin of future events every time it
moves.
As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
