V3: ESM+CJS, automatic split combined cookies, & general API cleanup

[nfriedly]

This has a few big changes all rolled into one:

• Converted the library to ESM and added a script to automatically build a CJS version on pre-commit.
  • I think I got everything right in package.json to make it work in either type of project.
• splitCookieString() is now called automatically when appropriate, with a new split option to override the behavior
• The documented API is now a single named export: parseSetCookie(input, options)
  • but all previous API methods/names remain present for backwards compatibility - in both the CJS and ESM versions

I think this will be a non-breaking change for most, if not all, users. But I'm not 100% sure and I had previously stated that the automatic splitCookieString() would be in a major version, so calling this 3.0 feels like the right move.

@bytesnz, @thib3113, @realityking, @benmccann, @renatoaraujoc, & @LenweSaralonde would you each mind giving this a shot sometime in the next week or two? (Or let me know if you need more time than that.)

You can install this branch in your local project with this command:

npm install git+https://github.com/nfriedly/set-cookie-parser#v3

Fixes #73
Fixes #50
Relates to #68

[nfriedly]

This is just a copy of of lib/set-cookie.js, but with the exports at then end changed to cjs.