Build using Babel & Rollup:

* samples
	https://github.com/PolymerLabs/lit-element-build-rollup/blob/master/package.json
	https://github.com/PolymerLabs/lit-element-build-rollup/blob/master/rollup.config.js
	https://43081j.com/2018/09/polymer-lit-with-rollup

* use LINUX commands such as rm -rf for dirs, cp -r --parent path/files build for recursive copying to target, restoring path
	https://stackoverflow.com/questions/1529946/linux-copy-and-create-destination-dir-if-it-does-not-exist

* If getting [Object] or part => ... then we're most likely including multiple copies of lit-html
	https://github.com/Polymer/lit-element/issues/390
	/node_modules/lit-element/node_modules/lit-html <= Delete that folder, not sure why it's there?

* Using Polymer CLI: make sure to use --npm flag
	https://polymer-library.polymer-project.org/3.0/docs/tools/polymer-cli-commands#build