Transaction for entities proceeded by RXJava observer with DBFlow

DBFlow Version: 5.0.0-alpha1

Bug or Feature Request: Question

Description:

How to use DBFlow transaction for RXJava observer so that the transaction is for whole stream of items proceeded by the observer? My attempt is:
```
new Observer() {
@Override
public void onSubscribe(@NonNull Disposable d) {
FlowManager.getDatabase(AppDatabase.class).beginTransaction();
}

@Override
public void onNext(@NonNull Item item) {
FlowManager.getModelAdapter(Item.class).save(item, FlowManager.getDatabase(AppDatabase.class));
}

@Override
public void onError(@NonNull Throwable error) {
}

@Override
public void onComplete() {
FlowManager.getDatabase(AppDatabase.class).endTransaction();
}
};
```

But beginTransaction() blocks processing of items.