Publish version without polyfilled async

[jonluca]

The published version on npm uses babel to polyfill async/await with regeneratorRuntime.

It would be great to either publish A) a version that lets us import from source, and let our bundler deal with figuring out what needs to be polyfilled, what ES verison we want to target, etc or B) Publish a version without legacy browser support

Would lead to both bundle size improvements and speed improvements.