Add ESLint and TypeScript

[pmbanugo]

Closes https://github.com/vercel/micro/issues/457

This PR adds TypeScript and rewrites the library code using TypeScript.

Highlight:

• Rewrote the library using TS
• Rewrote the test using TS and node-tap
• Updated the GitHub Actions
• Generate types for the library
• Removes deprecated endpoints
• Drops Node.js 12 support

[leerob]

Amazing! Will dive into this and take a look.

[pmbanugo]

Hi @leerob It's ready for review.

[leerob]

I think we'll need to add a test script for CI.

[pmbanugo]

I think we'll need to add a test script for CI.

@leerob I've updated the script, it should work now.

[pmbanugo]

That should work but it's failing 😓 I'm not sure why, but I'll check again.

[pmbanugo]

@leerob Updated... If it doesn't work this time, perhaps you can try clearing the cache and rerunning the build.

[leerob]

It works! 🎉

[pmbanugo]

Will try to get one more review on here tomorrow, but LGTM.

Hi, @leerob just following up on this 😄

[leerob]

Planning to go ahead and merge/release https://github.com/vercel/micro/pull/460, and then let's release this as a major version 👍

[pmbanugo]

@leerob Do you want me to update my branch and use the reverted change, or go ahead with what I currently have with serve and http.Server? I guess you would want the second option as part of the major version release.

[leerob]

What do you think? I think we probably keep the breaking changes.

[pmbanugo]

I think we keep the breaking change because that way we can use it programmatically with fastify or something similar. I'll make the necessary changes and update the PR soon.

[pmbanugo]

I left it with the breaking change and updated the documentation