GitHubFileSystem should use GitHub API

[jbfaden]

GitHub provides an API to get directory listings. (Thanks, ChatGTP for clearly demonstrating this.) Try for example:

curl https://api.github.com/repos/autoplot/dev/contents/bugs/2025

This returns a JSON listing of the files and folders within 2025 along with hashes.

[jbfaden]

See #94

[jbfaden]

See https://chatgpt.com/share/685579ed-dcfc-800c-9d89-5828be1f5fda

[jbfaden]

ChatGPT also showed how to list GitLab:

dot21-9> curl  'https://research-git.uiowa.edu/api/v4/projects/abbith%2Fjuno/repository/tree?path=u&ref=main'| json_pp

[jbfaden]

I couldn't get research-git to work any more than listing abbith/juno. I need to experiment with how to determine which part of the URL is the project and which is the directory within the project. I'll do this after GEM.

[jbfaden]

The problem was I didn't account for when the branch name is in the path. research-git abbith/juno works for this case now.

[jbfaden]

I had given up on it working with my gitlab instance. This works, showing maybe I could get it to work:

saturn> curl "http://git.jfaden.net/api/v4/projects?visibility=public" | json_pp