Add module to package.json

[denisx]

What issue does this pull request resolve?

To emulate esm build, you need couple thing at package.json: module and sideeffects

What changes did you make?

Bundlers will cut unused code better then now. Goog for named imports.

[denisx]

@eventualbuddha @Delapouite hello here! )

[jasoniangreen]

Thanks for your contribution @denisx. This change seems to be correct to me, just give me some time to double check.