Fix EnforceRateLimit
Fix EnforceRateLimit

Not resetting _requestsThisBurst meant that after 30 calls to the Reddit API you would only be able to make one call per minute. I fixed this by resetting _requestsThisBurst to 0 when _burstStart is reset.

Not making the method synchronized meant that there existed a race condition where more than 30 requests would be transmitted every 60 seconds. This can be exhibited by printing _requestsThisBurst on every EnforceRateLimit call and making a demo program that calls the API many times in parallel, for example

```var posts = reddit.GetSubreddit("askreddit").Hot.Take(100);
Parallel.ForEach(posts, post =>
{
    var topCommentAuthor = post.Comments.FirstOrDefault().Author
});```

CrustyJew/RedditSharp,IAmAnubhavSaini/RedditSharp,RobThree/RedditSharp,pimanac/RedditSharp,tomnolan95/RedditSharp,angelotodaro/RedditSharp,nyanpasudo/RedditSharp,justcool393/RedditSharp-1,theonlylawislove/RedditSharp,chuggafan/RedditSharp-1,SirCmpwn/RedditSharp,Jinivus/RedditSharp