[added] withMerge to /operators
Summary: Related: https://github.com/material-motion/material-motion-js/issues/114
Reviewers: O2 Material Motion, O3 Material JavaScript platform reviewers, Material Motion, featherless
Reviewed By: O2 Material Motion, Material Motion, featherless
Tags: Material Motion
Differential Revision: http://codereview.cc/D3023