Experiment with render filtering
Take a new selection-based tack on targeted re-rendering
Tweak number of elements in example
Have top-level render return the selection created so we can use it to rerender later
Move workhorse render function out of Spec class
Preserve indices of data items when redrawing selectively
Move sample code to a separate file, use numeric indexing for shape types
Merge branch 'experimental-render-filtering'

Conflicts:
	test.html