Make graphql closer to cli

[wd60622]

Describe what this PR does / why we need it

This allows use of graphql API to be a bit closer to the CLI

For instance, gh api graphql -f query=<query> -F login=<login> -F repo=<repo> is :

local gh = require "octo.gh"

gh.api.graphql {
  f = { query = query },  
  F = { login = login, repo = repo }, 
}

The previous behavior still exists:

gh.api.graphql {
  query = query, 
  fields = { login = login, repo = repo },
}

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

Special notes for reviews

Checklist

• Passing tests and linting standards
• Documentation updates in README.md and doc/octo.txt