Add rate limit awareness

We use the v4 github API to limit the amount of information returned and the number of queries that need to be made. However, it is still possible with large repos to hit rate limits. It would be ideal to track this information with each query and be smart about retries with the information gleaned from the rate limit section of the responses.

The issue names no files or tests. Start by locating the v4 GitHub API query and response handling; done means rate-limit data is tracked per query and retries use the response's rate-limit information.

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