Refactor how timing code works.
Refactor how timing code works.

Support scheduling functions, not just testharness test objects.
Always have a dummy t=0 object.

Fixes #224

beni55/web-animations-js-legacy,beni55/web-animations-js-legacy,web-animations/web-animations-js-legacy,beni55/web-animations-js-legacy,web-animations/web-animations-js-legacy,web-animations/web-animations-js-legacy,beni55/web-animations-js-legacy,birtles/web-animations-js,birtles/web-animations-js,birtles/web-animations-js