Add support for ES6 module import

Hi!

I think it would be nice if select was available as an ES6 module. The hidden goal for me is having clipboard.js available as an ES6 module (fixing https://github.com/zenorocha/clipboard.js/issues/568).

As with select I suggest:

Putting the ESM version as source in /src
Using rollup to generate the CJS (current source) version in /cjs
Verify that tests passes using the same karma and test suite, but taking as source the CJS version (to verify it's still valid).

What do you think?

zenorocha / good-listener