Get Top Ranks
<void> leaderboard.getTopRanks(<Integer> limit, <Function> success, <Function> failure);
where:
limitis a number of entries to fetch, maximum 50, default 10.
“success” callback is passed array of rank objects.
[{"public_id": <public id>,"rank": <rank>,"name": <name>,"score": <score>,"level": <level>,"public_data": <public data>},{"public_id": <public id>,"rank": <rank>,"name": <name>,"score": <score>,"level": <level>,"public_data": <public data>}...]
