cg-renderer gains a regions slot; the text/svg treatments get real
draw/hit methods; cg-regions-hit + cg-render-apply complete the loop.
Prototype on solitaire: cg-sol--svg returns (image . regions), redisplay
goes through cg-render-game, and [mouse-1] selects-and-acts by reusing the
keyboard pick-up/drop. Adds cgt-keystone-regions; suite 110/110.