[INPROGRESS] First version of tokumx converter

This pull request aims to add tokumx support to mongoriver by converting tokumx oplog records to mongo oplog records.

cc @ebroder 
The GTID is 2 integers concatenated together and binary-encoded (http://www.tokutek.com/2014/04/on-tokumx-oplog-tailable-cursors-and-concurrency/ mostly covers it). It is guaranteed to be monotonically increasing.