CSHARP-1037: Use int? consistently for optional MaxBatchCount and similar properties.
CSHARP-1074: Reimplement MongoCollection Distinct using Core operation.
CSHARP-1074: Code review changes to MongoCollection Distinct.
CSHARP-1051: Added ConfigureAwait(false) to all uses of await in the library projects (but not the test projects).
CSHARP-1074: Reimplement MongoCollection Group using operation in Core.