Add ALBERT to AutoClasses
Author: eladsegal
Pull request: yes

Adds ALBERT to AutoClasses and also fixes some documentation mistakes along the way

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1995?src=pr&el=h1) Report
> Merging [#1995](https://codecov.io/gh/huggingface/transformers/pull/1995?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/1ab8dc44b3d84ed1894f5b6a6fab58fb39298fc7?src=pr&el=desc) will **increase** coverage by `1.22%`.
> The diff coverage is `31.25%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/1995/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1995?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #1995      +/-   ##
==========================================
+ Coverage   82.83%   84.06%   +1.22%     
==========================================
  Files         105      105              
  Lines       15545    15561      +16     
==========================================
+ Hits        12877    13081     +204     
+ Misses       2668     2480     -188
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/1995?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/modeling\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX2F1dG8ucHk=) | `30.61% <20%> (-1.21%)` | :arrow_down: |
| [transformers/tokenization\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rva2VuaXphdGlvbl9hdXRvLnB5) | `45% <33.33%> (-0.95%)` | :arrow_down: |
| [transformers/configuration\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL2NvbmZpZ3VyYXRpb25fYXV0by5weQ==) | `60% <66.66%> (+0.54%)` | :arrow_up: |
| [transformers/modeling\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX29wZW5haS5weQ==) | `82% <0%> (+1.33%)` | :arrow_up: |
| [transformers/modeling\_ctrl.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX2N0cmwucHk=) | `96.47% <0%> (+2.2%)` | :arrow_up: |
| [transformers/modeling\_xlnet.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3hsbmV0LnB5) | `73.61% <0%> (+2.43%)` | :arrow_up: |
| [transformers/modeling\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3JvYmVydGEucHk=) | `71.76% <0%> (+12.35%)` | :arrow_up: |
| [transformers/tests/modeling\_tf\_common\_test.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL21vZGVsaW5nX3RmX2NvbW1vbl90ZXN0LnB5) | `97.08% <0%> (+15.53%)` | :arrow_up: |
| [transformers/modeling\_tf\_pytorch\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/1995/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX3B5dG9yY2hfdXRpbHMucHk=) | `95.13% <0%> (+85.41%)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1995?src=pr&el=footer). Last update [1ab8dc4...a415156](https://codecov.io/gh/huggingface/transformers/pull/1995?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).


Thank you, that's great!