[AB-219] Progress bar
## This PR:
- adds progress bars to tokenization
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2131?src=pr&el=h1) Report
> Merging [#2131](https://codecov.io/gh/huggingface/transformers/pull/2131?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/6a73382706ce3c6905023872f63a680f0eb419a4?src=pr&el=desc) will **decrease** coverage by `0.25%`.
> The diff coverage is `96%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2131/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2131?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2131      +/-   ##
==========================================
- Coverage   80.07%   79.82%   -0.26%     
==========================================
  Files         112      113       +1     
  Lines       16867    16885      +18     
==========================================
- Hits        13506    13478      -28     
- Misses       3361     3407      +46
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2131?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/timing.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3RpbWluZy5weQ==) | `100% <100%> (ø)` | |
| [transformers/tokenization\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl91dGlscy5weQ==) | `91.09% <100%> (+0.07%)` | :arrow_up: |
| [transformers/tokenization\_bert.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl9iZXJ0LnB5) | `95.57% <88.88%> (-0.36%)` | :arrow_down: |
| [transformers/tokenization\_albert.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl9hbGJlcnQucHk=) | `82.9% <0%> (-6.84%)` | :arrow_down: |
| [transformers/tokenization\_xlnet.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl94bG5ldC5weQ==) | `84% <0%> (-6.41%)` | :arrow_down: |
| [transformers/tests/modeling\_tf\_common\_test.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL21vZGVsaW5nX3RmX2NvbW1vbl90ZXN0LnB5) | `93.33% <0%> (-3.59%)` | :arrow_down: |
| [transformers/tests/tokenization\_tests\_commons.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL3Rva2VuaXphdGlvbl90ZXN0c19jb21tb25zLnB5) | `97.41% <0%> (-2.59%)` | :arrow_down: |
| [transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL2ZpbGVfdXRpbHMucHk=) | `37.5% <0%> (-2.5%)` | :arrow_down: |
| [transformers/hf\_api.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL2hmX2FwaS5weQ==) | `95% <0%> (-2.5%)` | :arrow_down: |
| [transformers/tests/modeling\_common\_test.py](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL21vZGVsaW5nX2NvbW1vbl90ZXN0LnB5) | `73.24% <0%> (-1.3%)` | :arrow_down: |
| ... and [3 more](https://codecov.io/gh/huggingface/transformers/pull/2131/diff?src=pr&el=tree-more) | |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2131?src=pr&el=footer). Last update [6a73382...a4d0bc7](https://codecov.io/gh/huggingface/transformers/pull/2131?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
