Implement Rate limit checking

[schochastics]

To implement pagination (#41), we need to keep track of rate limits

[chainsawriot]

We can expose the headers (or at least some headers field) within make_get_request. The least destructive way is to make it attr

headers <- httr::headers(request_results)
output <- httr::content(request_results)
attr(output, "headers") <- headers
return(output)

[schochastics]

I was thinking that too.I will built that into the refactoring in #31. We then have a preliminary wiki page which can explain how to paginate accessing the attribute and we built a robust solution later. I think this needs a bit more time to come up with a good solution

[schochastics]

rate limits are now returned in the attribute "headers" of the output

[schochastics]

still need a function to explicitly check the rate limit

[schochastics]

No endpoint exists to check the ratelimit. ratelimit is only returned in the header of a get request.