db.coll.update(
               { item: "ZZZ135" },
               {  item: "ZZZ135",  stock: 5,  tags: [ "database" ] },
               {upsert: true}
              )

WriteResult({
    "nMatched" : 0,
    "nUpserted" : 1,
    "nModified" : 0,
    "_id" : ObjectId("54455f33b247e073d7161b32")
})

bool
mongoc_collection_command_simple (mongoc_collection_t       *collection,
                                  const bson_t              *command,
                                  const mongoc_read_prefs_t *read_prefs,
                                  bson_t                    *reply,
                                  bson_error_t              *error);

bool mongo::DBClientWithCommands::simpleCommand     (   const std::string &     dbname,
        BSONObj *   info,
        const std::string &     command
    )