Allow access to response headers, especially in errors

[jfsiii]

This is most valuable for rate limit errors. Currently, the error object when a client is rate limited is:

{ [Error: HTTP Error 400: Bad Request]
  statusCode: 400,
  data: '{"error":"Rate limit exceeded. Clients may not make more than 350 requests per hour.","request":"\\/1\\/lists.json?screen_name=JFSIII&cursor=-1"}' }

However, this doesn't inform the client when their limiting will end. That information is available via the X-RateLimit-Reset header. The value is the UNIX timestamp when the limit will be lifted.

Even successful connections have useful information. Most notably X-RateLimit-Remaining which informs the client how many calls are left before they get limited.

I'm just getting started with this library, so I don't have any suggestions for the preferred way to make them available. I only know that they are a requirement for clients. They are so important, I feel like I must have missed their inclusion. If so, I apologize for the noisy ticket and ask that you point me to the documentation or provide some example code.