Feature Request: Support esmodule

[magiziz]

Description

We have been shipping awesome features with i18n-js. But we also encountered some of the issues with esmodule when people were downloading our package and it didn't work well. We say that from here: fnando/i18n#44 (comment)

But we also went with your appraoch too: fnando/i18n#44 (comment)

I feel like i can help you raise a PR on this repo if you can show me how you want me to update it. I was thinking of going with the same approach as this guy suggested: fnando/i18n#44 (comment)

But let me know what you think 👍

[magiziz]

Also want to address this too. Locally this works fine, but when we ship it externally then it doesn't point out well and people might get this bug too:

`import { I18n } from "i18n-js";
         ^^^^
SyntaxError: Named export 'I18n' not found. The requested module 'i18n-js' is a CommonJS module, which may not support all module.exports as named exports.
CommonJS modules can always be imported via the default export, for example using: