Abstract and encapsulate gateway checking logic from this package and JayBrown/Tools/tree/master/ipfg

[SgtPooki]

In the readme, we state:

A CLI version ipfg is available here: https://github.com/JayBrown/Tools/tree/master/ipfg

I propose we encapsulate the logic in this repo into its own encapsulated logic so that one could run the check in both the browser and via CLI, but also via other packages.

It would also make sense to support the often requested "gateway race" logic within this package.

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[SgtPooki]

@lidel thoughts?

[lidel]

SGTM.

I will be writing HTTP Gateway specs, and want to have a compliance test suite for HTTP gateway that tests against that spec.

Some tests are really easy to do outside of browser, so I am not sure if we will have 100% code resuse, but even if we could have 80% of code that can run in both browser and CI that is a big win.

First step would be to extract logic and run tests on GithubAction CI, testing PRs submitted against this repo and failing if gateway is offline or does not support IPNS.