Added ability to get comments from from the post class.

The commit comparison shows a new file so ill try and breakdown the changes.

New method on Post with the following sig

```
public List<Comment> GetComments()
```

New code in constructor of Comment

```
public Comment(Reddit reddit, JToken json)
            : base(reddit, json)
        {
            var data = json["data"];

            Author = data["author"].Value<string>();
            Created = Reddit.UnixTimeStampToDateTime(data["created"].Value<double>());
            Content = data["body"].Value<string>();
            ContentHtml = data["body_html"].Value<string>();
            Downvotes = data["downs"].Value<int>();
            Upvotes = data["ups"].Value<int>();
            Reddit = reddit;

            //Parse sub comments
            Comments = new List<Comment>();
            if (!string.IsNullOrEmpty(data["replies"].ToString()))
                foreach (var comment in data["replies"]["data"]["children"])
                    Comments.Add(new Comment(reddit, comment));

        }
```