Create a library that can be imported

[Titaniumtown]

I whipped up this "library version" of main.py which can be imported. So one could just import it like: from artifact_lib import get_latest_artifact_url

[Titaniumtown]

I've added a check for seeing if you've hit your rate limit for the github api. Should be a temp fix for errors thrown by #4

[JayFoxRox]

This PR adds a lot of redundancy. However, adding redundancy is not acceptable in my opinion (especially if we have issues like #4 or #3 which now affect the duplicated code).
Instead, this should replace the existing main.py (or slim it down to where it only uses this library) and deal with packaging (like a typical Python module / library).

An API might also not be suitable until we figure out #1 so that the API could remain stable.
I see that you added the parameters to the functions, but that doesn't feel like the Python-way to go about it.
It was fine for a dirty hack like the original tool, but it's not acceptable for a long-term solution like a Python module / library.

[Titaniumtown]

This project is just something I'm using for a little project of mine (https://github.com/Titaniumtown/yatopia-autoupdate) a minecraft server updater, that auto-fetches the latest artifact of a specific branch.

[JayFoxRox]

That's all fine, but I don't think your changes are upstreamable (to this project) for the reasons I described before.
I'm suprised that your script works for you (does it? how do you authenticate?)

With the master branch, I keep getting this for my own repositories (which is the issue described by #4):

{
  "message": "You must have the actions scope to download artifacts.",
  "documentation_url": "https://docs.github.com/rest/reference/actions#download-an-artifact"
}

So the HTTP server would have to be a logged in GitHub User of some form, which is not acceptable to me.
Even if that was done, we'd be running into actions/upload-artifact#51 (which means any generated URLs don't work, unless we act as a proxy for guest users).

I don't see how your modifications would work around this problem, or how your repository can be configured to avoid this?