v2.0.0

• The underlying *http.Client is now passed as an option when initializing a client.
• Use value type instead of pointer for credentials when initializing a client.
• Add DefaultClient() method which returns a valid, read-only client with limited access to the Reddit API. To create a custom one, NewReadonlyClient() can be used.
• Remove the before anchor from responses.
• The decoding process for a listing response has been revamped, and the after anchor is now included in the *Response object. For example, when fetching a user's comments, instead of getting a struct containing the list of comments, and the after value, you now get the list of comments directly, and the after can be obtained from the *Response.
• Create WikiService, LiveThreadService, and WidgetService.
• Add more methods to SubredditService, ModerationService, and FlairService.
• Add error handling for rate limit errors (*RateLimitError).