[run_lm_finetuning] Train from scratch
Ability to train a model from scratch, rather than finetune a pretrained one.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2570?src=pr&el=h1) Report
> Merging [#2570](https://codecov.io/gh/huggingface/transformers/pull/2570?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/65a89a89768f5922e51cdc7d49990d731e3f2c03?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2570/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2570?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #2570   +/-   ##
=======================================
  Coverage   74.61%   74.61%           
=======================================
  Files          87       87           
  Lines       14802    14802           
=======================================
  Hits        11044    11044           
  Misses       3758     3758
```



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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2570?src=pr&el=footer). Last update [65a89a8...55939b5](https://codecov.io/gh/huggingface/transformers/pull/2570?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Looks good to me, feel free to merge it when you feel ready @julien-c <|||||>Yo! merge this shit up!!  <|||||>Thanks, A Lot Guys your the best!