[collections] An order statistic tree

[Rodion Efremov]

Hello, all.
I would like to announce that I have a java.util.Set implementation that is an 
order statistic tree (all non-bulk operations + select + rank in O(log n) time) 
[1]. However, it seems like the team on behalf of the order statistic tree 
issue is rather idle [2], hence the message.
Best,
rodde
[1] https://github.com/coderodde/OrderStatisticTree
[2] https://issues.apache.org/jira/browse/COLLECTIONS-479