Revamp listing decoding, include after/before anchors in response

Now, instead of returning an object containing a list of results + the
anchors, we return just the list. The anchors are available in the
response object. Much cleaner this way in my opinion

go-github and godo do it this way too. They include some meta
information in the returned response objects

Signed-off-by: Vartan Benohanian <vartanbeno@gmail.com>

reddit/emoji.go

@@ -252,7 +252,7 @@ func (s *EmojiService) Upload(ctx context.Context, subreddit string, createReque
 
 	err = CheckResponse(httpResponse)
 	if err != nil {
-		return &Response{httpResponse}, err
+		return newResponse(httpResponse), err
 	}
 
 	return s.upload(ctx, subreddit, createRequest, fields["key"])