Handle GitHub Rate Limiting and Abuse Rate Limiting

[adamzolyak]

Proposed implementation:

• Send requests in batches (ex. 20) with a 1 second pause between batches.
• Check for HTTP 4xx.
• If HTTP 4xx, check X-RateLimit-Remaining and Retry-After headers.
• If X-RateLimit-Remaining < number of HTTP calls required, stop and output console message.
• If Retry-After wait number of seconds specified before sending additional requests.

I also feel like I've seen HTTP 401 during normal (non-abuse) rate limiting. Investigate more and handle if needed.

[adamzolyak]

suggestion to resolve #4

[iandouglas]

const response = await context.github.issues.create({})
console.log(response.meta)

// output:
{
  "x-ratelimit-limit": 5000,
  "x-ratelimit-remaining": 4999,
  "x-ratelimit-reset": 1544635447,
}

there may be additional headers like x-retry-after in there as well.