BLUE
Author: anhnt170489
Pull request: yes

In this PR: 
- I add BertForMultiLabelClassification, RobertaForTokenClassification, RobertaForMultiLabelClassification. 
- I add examples for Finetuning the BERT, RoBERTa models for tasks on BLUE (https://github.com/ncbi-nlp/BLUE_Benchmark). BLUE (Biomedical Language Understanding Evaluation) is similar to GLUE, but for Biomedical data. The "run_blue", "utils_blue" are customized from "run_glue", "utils_glue", but more sufficient, because it contains not only sequence classification, but also token classification, multi-label classification. People may also have more options for examples of fine-tuning BERT/RoBERTa. 
- I also add test function to test_examples as well as test data (HOC)  

Comments:
@LysandreJik @julien-c one of you want to give a look?

# [Codecov](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=h1) Report
> Merging [#1238](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/pytorch-transformers/commit/2c177a87eb5faab8a0abee907ff75898b4886689?src=pr&el=desc) will **decrease** coverage by `0.43%`.
> The diff coverage is `30.88%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #1238      +/-   ##
==========================================
- Coverage   81.23%   80.79%   -0.44%     
==========================================
  Files          57       57              
  Lines        8029     8092      +63     
==========================================
+ Hits         6522     6538      +16     
- Misses       1507     1554      +47
```


| [Impacted Files](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pytorch\_transformers/modeling\_bert.py](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238/diff?src=pr&el=tree#diff-cHl0b3JjaF90cmFuc2Zvcm1lcnMvbW9kZWxpbmdfYmVydC5weQ==) | `85.68% <27.27%> (-2.65%)` | :arrow_down: |
| [pytorch\_transformers/modeling\_roberta.py](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238/diff?src=pr&el=tree#diff-cHl0b3JjaF90cmFuc2Zvcm1lcnMvbW9kZWxpbmdfcm9iZXJ0YS5weQ==) | `62.33% <32.6%> (-12.9%)` | :arrow_down: |
| [pytorch\_transformers/tests/modeling\_common\_test.py](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238/diff?src=pr&el=tree#diff-cHl0b3JjaF90cmFuc2Zvcm1lcnMvdGVzdHMvbW9kZWxpbmdfY29tbW9uX3Rlc3QucHk=) | `73.19% <0%> (-0.13%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=footer). Last update [2c177a8...3cbe79a](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1238?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).


@thomwolf : Hi, all checks have passed. Please review it again ;). 

This PR is out of date. 
I updated a new one here (https://github.com/huggingface/transformers/pull/1440).