Reworded and made minor adjustments in README.md
Changed onupdate() to be called after values are updated
Changed tweens created with <= 0 time to finish immediately
Fixed flux.update() to not call easing func if progress is >= 1

This avoids precision errors in the easing function leaving the final
value as something very close to the destination value, rather than the
actual destination value.
Fixed :after() to inherit last tween's parent

This fixes multiple-chained :after() functions