refactor: Convert to TypeScript

[fb55]

Initial big lift to convert the codebase, broken into three commits to make the bigger changes obvious. Everything seems to work now, including detection if users pass selectors ($('<div>') will product a Cheerio<Node> type, $('.foo') a Cheerio<Element>).

Currently missing:

• The ergonomics of using types aren't great. We should re-export all regularly used types.
• We can now use typedoc to generate our documentation. Produced docs still have to be improved:
  • Examples now need to be put in code blocks.
  • The organization is very hard to grasp.
• Benchmarks have to be updated to use ts-node.

[voxpelli]

Exciting stuff @fb55! Great work 🎉

[XhmikosR]

@fb55 sorry for the CC on an old PR, but I didn't want to make a new issue just for this. Is there any reason you didn't go with ES2017 or whatever is equivalent for Node.js 10, which is the oldest supported Node.js version?

[XhmikosR]

Ah, NVM I see now that the package.json engines is set to >=6. On CI Node.js >= 10 is tested hence why I thought this could be improved. IMHO, these two should be in sync, especially since Node.js 6 is ancient...

[fb55]

Jest doesn't support Node 6, which is why Node 6 isn't part of the CI anymore.

I am still a bit hesitant to bump the Node version, primarily due to the discussion in #1585. But the mismatch between CI and package.json seems like a good reason to make the cut.

[XhmikosR]

Ah, now I remember, thanks for the info.

So, yeah, not sure what the proper semver way would be. Perhaps release v1.0.0 final with the current engines, and then cut a new v2.0.0 with the bump in engines and tsconfig.