Add Tween example and hacky runtime.start(when) mechanism.

Authored by featherless on Mar 16 2017, 1:13 PM.

Description

Add Tween example and hacky runtime.start(when) mechanism.

Reviewers: O2 Material Motion, O4 Material Apple platform reviewers, Material Motion

Tags: Material Motion

Differential Revision: http://codereview.cc/D2886