CSHARP-790: Added support for $maxTimeMS to limit the time the server should spend on an operation.
CSHARP-790: Remove MaxTime from settings; it can only be set at the individual operation level. Added support for MaxTime to AggregateQuery, Count, Eval and MapReduce.
CSHARP-790: Changed implementation of Aggregate to use AggregateArgs. Added support for MaxTime to Count, FindAndModify, FindAndRemove and Eval.