Implement rate limit management functionality

We should also consider implementing the rate limit API.

Which will be helpful to check how many rate_limit is remaining and then we can avoid the rate limit exceeded error by doing a sleep(time-interval) method until we re-gain the rate-limit.

E.g. While using a search API we only get 30 rate_limit/minute; Now, suppose that we have a list of 1000 contributors and we have to perform a search for each. So, what we can do is, we can check if the search_rate_limit remaining is 1 then sleep(60). see;

Or it would be better if we could implement the whole process in IGitt itself.