CSHARP-797: Eliminated BulkModify folder and moved classes that were in that folder to the Operations folder.
CSHARP-797: Renamed BulkModify to BulkWrite to be more consistent with server terminology.
CSHARP-797: Renamed ModifyMethod to WriteMethod.
CSHARP-797: Renamed ModifyRequest to WriteRequest.
CSHARP-797: Some refactoring internal to BulkWriteOperation.
CSHARP-797: Renamed some mis-named variables.