[Reformer] Include char lm to Trainer
Trainer currently expects every model to have a tokenizer. The reformer: `google/reformer-enwik8` is a char lm which does not require a tokenizer.
@patrickvonplaten Thank you your awesome work. I´m super excited about a char-lm. 
I´m trying to can  train the "reformer" model, using the "google/reformer-enwik8".

But using this script or the run_language_modeling.py I get the error about the lack of tokenizer ( that is expected to a char only LM).
`Model name 'google/reformer-enwik8' was not found in tokenizers`

Can you give me some pointer how I could train it?<|||||>Hi bratao! Good point I will consult with our team on how to include models that don't have don't need a tokenizer! Let me get back to you in a couple of days :-) 