Upgrade syntax to ES modules

[rootwork]

Type of feature

• New functionality
• Performance
• Code refactoring (e.g. to be simpler or easier to understand)
• Developer Experience (DX)
• Other (please describe below)

Describe the feature

Several dependencies are now ES-only imports, so it makes sense to upgrade Premail to use ES syntax as well.

This seems to be a pretty good guide:
https://electerious.medium.com/from-commonjs-to-es-modules-how-to-modernize-your-node-js-app-ad8cdd4fb662

Preferred solution

No response

Alternatives

No response

Related code

No response

Additional context

package.json will need to be updated with entry points; there is debate whether ESM, transpiled or both should be included in the npm package:

https://stackoverflow.com/a/52509974
https://survivejs.com/maintenance/packaging/anatomy/#entry-points

If the feature request is approved, would you be willing to submit a Pull Request?

• Yes
• No

[rootwork]

It looks like unless we want to run things with the --experimental-modules flag, this will require Node 14.x or above. Which means it's blocked on #56, and will be a major version bump.

[github-actions]

There hasn't been any activity on this issue recently, and in order to prioritize active issues, it is being marked as stale.

Please make sure to update to the latest version and check if that solves the issue. Let us know if that works for you by leaving a 👍

Because this issue is marked as stale, it will be closed and locked in 10 days if no further activity occurs. If you want to prevent it from being closed, just leave a comment.

Thank you for your contributions!

[github-actions]

There hasn't been any activity on this issue recently, and in order to prioritize active issues, it is being marked as stale.

Please make sure to update to the latest version and check if that solves the issue. Let us know if that works for you by leaving a 👍

Because this issue is marked as stale, it will be closed and locked in 10 days if no further activity occurs. If you want to prevent it from being closed, just leave a comment.

Thank you for your contributions!

[github-actions]

Issue closed and locked due to lack of activity.
If you encounter this same issue, please open a new issue and refer to this closed one.