Migrate to TypeScript

[jahed]

To avoid using unsupported Node APIs and dealing with version compatibility, migrate to TypeScript and add a build step.

It might be convenient at this point to switch to async/await and drop @jahed/promises for better readability.

[jahed]

Tried migrating:

5a5a7ca

Because the package relies on an install hook which points to a lib file, it's a sort of a chicken and egg problem. I need to install deps to build, but the install step involves running a built file.

I could use --ignore-scripts for CI installs but that will ignore all scripts, including dev dependencies which may need them. I tried the various hook but NPM/Yarn lifecycle hooks are inconsistent across versions and it's a minefield knowing what executes only locally and in production.