add ElementCreator interface+impl to mitigate danger of passing Document params.
add a test for keyTimes+keySplines.
[huge] thread svg.ElementCreator param through the entire library. Document why.
update .gitignore.
remove svg.Builder.build(), since it's a no-op now.
svg.Tbreak: subclass svg.Element to get standard setters.
rename svg.Builder => svg.ElementHandler.
demo: improve the spiral demo with proper use of <use>.
svg.animateTransform: fix incorrect type string.
demo: animate the spiral demo, showing how bad the current API is.