[marian] converter supports models from new Tatoeba project
- no state dict change, just need to read model metadata from a new path
- we only accept models with 7 letter names... like `ara-eng`. This is the new format.
- added integration test for `ara-eng`

Done:
- [x] upload 300 models: all new ones that were not "dominated" by a model we already have, where dominated means same langpair but the first model has a higher BLEU score.

Todo: 
- [ ] switch integration test for `ara-eng` -> `ar-en`.
- [ ] automated model cards with correct `tags`, more info on all possible language codes.
- [ ] automated conflict resolution: Don't convert models that are worse than predecessors.
- [ ] decide what to do about naming: move all to 3 letter/all to 2 letter?
- [ ] notebook -> pyfile
- [ ] tweet 

cc @julien-c 


Dict where keys are old names, and values are new names, filtered to situations where new name has higher BLEU than old name:
```
{'bg-es': 'bul-spa',
 'es-eu': 'spa-eus',
 'eu-es': 'eus-spa',
 'es-bg': 'spa-bul',
 'ilo-en': 'ilo-eng',
 'es-mk': 'spa-mkd',
 'es-ca': 'spa-cat',
 'es-af': 'spa-afr',
 'lt-es': 'lit-spa',
 'bn-en': 'ben-eng',
 'th-en': 'tha-eng',
 'fr-ca': 'fra-cat',
 'ga-en': 'gle-eng',
 'en-ga': 'eng-gle',
 'ko-fi': 'kor-fin',
 'es-uk': 'spa-ukr',
 'gl-es': 'glg-spa',
 'eo-sv': 'epo-swe',
 'ca-de': 'cat-deu',
 'az-en': 'aze-eng',
 'sv-eo': 'swe-epo',
 'de-is': 'deu-isl',
 'ceb-en': 'ceb-eng',
 'ca-fr': 'cat-fra',
 'tl-en': 'tgl-eng',
 'is-de': 'isl-deu',
 'ko-en': 'kor-eng',
 'is-es': 'isl-spa',
 'es-gl': 'spa-glg',
 'bg-fr': 'bul-fra',
 'de-af': 'deu-afr',
 'ko-es': 'kor-spa',
 'es-is': 'spa-isl',
 'af-es': 'afr-spa',
 'gl-en': 'glg-eng',
 'fi-en': 'fin-eng',
 'en-bg': 'eng-bul',
 'mk-es': 'mkd-spa',
 'ka-en': 'kat-eng',
 'en-eu': 'eng-eus',
 'de-ca': 'deu-cat',
 'ar-de': 'ara-deu'}
 
```
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6342?src=pr&el=h1) Report
> Merging [#6342](https://codecov.io/gh/huggingface/transformers/pull/6342?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/fb7330b30ebfbb3f07b87203f0405ee09905eeda&el=desc) will **increase** coverage by `0.99%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/6342/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/6342?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #6342      +/-   ##
==========================================
+ Coverage   78.42%   79.41%   +0.99%     
==========================================
  Files         156      156              
  Lines       28129    28129              
==========================================
+ Hits        22061    22340     +279     
+ Misses       6068     5789     -279     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/6342?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_mobilebert.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9tb2JpbGViZXJ0LnB5) | `24.55% <0.00%> (-72.36%)` | :arrow_down: |
| [src/transformers/generation\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3RmX3V0aWxzLnB5) | `84.21% <0.00%> (-1.26%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `86.31% <0.00%> (-0.98%)` | :arrow_down: |
| [src/transformers/modeling\_t5.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190NS5weQ==) | `83.71% <0.00%> (+0.18%)` | :arrow_up: |
| [src/transformers/modeling\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ191dGlscy5weQ==) | `87.35% <0.00%> (+0.19%)` | :arrow_up: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `82.44% <0.00%> (+0.25%)` | :arrow_up: |
| [src/transformers/tokenization\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdXRpbHMucHk=) | `90.40% <0.00%> (+0.40%)` | :arrow_up: |
| [src/transformers/generation\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3V0aWxzLnB5) | `96.94% <0.00%> (+0.83%)` | :arrow_up: |
| [src/transformers/configuration\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3V0aWxzLnB5) | `96.59% <0.00%> (+1.36%)` | :arrow_up: |
| [src/transformers/modeling\_distilbert.py](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19kaXN0aWxiZXJ0LnB5) | `97.82% <0.00%> (+1.63%)` | :arrow_up: |
| ... and [8 more](https://codecov.io/gh/huggingface/transformers/pull/6342/diff?src=pr&el=tree-more) | |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6342?src=pr&el=footer). Last update [fb7330b...c3288e2](https://codecov.io/gh/huggingface/transformers/pull/6342?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
