[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 
FTR, `private` operates on instance methods, but not class methods. You probably want http://www.ruby-doc.org/core-2.1.2/Module.html#method-i-private_class_method