Configuration Documentation
Author: LysandreJik
Pull request: yes

Updating the documentation with types, better naming, making sure every argument is listed and explained.

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2492?src=pr&el=h1) Report
> Merging [#2492](https://codecov.io/gh/huggingface/transformers/pull/2492?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/2b566c182efc5330e4753b6db74c5b0518716147?src=pr&el=desc) will **decrease** coverage by `0.18%`.
> The diff coverage is `0%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2492/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2492?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #2492      +/-   ##
==========================================
- Coverage   73.24%   73.06%   -0.19%     
==========================================
  Files          87       87              
  Lines       15009    15008       -1     
==========================================
- Hits        10994    10966      -28     
- Misses       4015     4042      +27
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2492?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/configuration\_xlm.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3hsbS5weQ==) | `96.15% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_gpt2.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2dwdDIucHk=) | `96.96% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_transfo\_xl.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3RyYW5zZm9feGwucHk=) | `92.3% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_bert.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2JlcnQucHk=) | `100% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3JvYmVydGEucHk=) | `100% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_albert.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2FsYmVydC5weQ==) | `100% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_distilbert.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2Rpc3RpbGJlcnQucHk=) | `100% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_mmbt.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX21tYnQucHk=) | `55.55% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_camembert.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX2NhbWVtYmVydC5weQ==) | `100% <ø> (ø)` | :arrow_up: |
| [src/transformers/configuration\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX29wZW5haS5weQ==) | `97.14% <ø> (ø)` | :arrow_up: |
| ... and [7 more](https://codecov.io/gh/huggingface/transformers/pull/2492/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/2492?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/transformers/pull/2492?src=pr&el=footer). Last update [2b566c1...6469f90](https://codecov.io/gh/huggingface/transformers/pull/2492?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).