Ability to build a `$` with additional properties about dax

[dsherret]

@andrewbrey yeah, you can just do what you showed there. I added a test for it in the PR too.

[andrewbrey]

If this API is added, many of the use-cases I would have for functions to add via the extras (helpers? plugins? worth bikeshedding over the name? 😄 ) object would want to have access to the constructed instance of $ in the function, i.e.:

const $ = build$({
  extras: {
    ghReleaseInfo(org, repo) {
      return $.request(`https://api.github.com/repos/${org}/${repo}/releases/latest`).json()
    },
  },
});

That should work with this "add extras during $ construction" API right? I'm pretty sure it will, but just wanted to put it on the radar for this enhancement request.