Fix demos to use 'transform' rather than '-webkit-transform'

From ec44a2bdc0a6220435cd7079e3b6546f3fa997ad onwards, the polyfill only
accepts 'transform'.
Fix test-circle-square.html demos after removal of parent argument from TimedItem constructors

See b2dda9802d9710a0b0563aaf478d0bfd584e3f6f
Update README.md and demos after change to KeyframeAnimationEffect

See 6a4d32eedc089e0b69b3b6f9201523bdf47d5313
Merge pull request #315 from steveblock/demos

Fix some demos