Refactored code to improve performance/employ best practices.
# What does this PR do?

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Refactors several segments of code in the ```scripts```,```src```,```tests```,```utils``` and ```setup.py``` and increases performance by a bit, using compression methods and newer practices.<br>
No new functions or methods/models added, therefore no documentation changes were required.


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [X] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
     Pull Request section?
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     to it if that's the case.
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      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?



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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
- research_projects/bert-loses-patience: @JetRunner
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Hello, and thank you for your contribution! It seems you were using a very outdated fork in order to open your PR (see the +5k -56k diff), as several files end up deleted and a lot of library improvements would be reverted were we to merge this PR.

In case these changes were intentional, let me point you to the following documentation: [**philosophy**](https://huggingface.co/transformers/philosophy.html).

The main idea is that all model/tokenizer code should be independent from other models/tokenizers. Manually editing, removing, or adding to a model or tokenizer should not impact any other whatsoever. This further allows to reduce the number of abstractions and gives access to the near-raw PyTorch/TensorFlow/Flax code of the models.

Finally, we have built [tools](https://github.com/huggingface/transformers/tree/master/utils) so that our maintenance isn't elevated by the high amount of duplicated code and so that our code coverage remains complete.

Thank you for your effort!<|||||>> Hello, and thank you for your contribution! It seems you were using a very outdated fork in order to open your PR (see the +5k -56k diff), as several files end up deleted and a lot of library improvements would be reverted were we to merge this PR.
> 
> In case these changes were intentional, let me point you to the following documentation: [**philosophy**](https://huggingface.co/transformers/philosophy.html).
> 
> The main idea is that all model/tokenizer code should be independent from other models/tokenizers. Manually editing, removing, or adding to a model or tokenizer should not impact any other whatsoever. This further allows to reduce the number of abstractions and gives access to the near-raw PyTorch/TensorFlow/Flax code of the models.
> 
> Finally, we have built [tools](https://github.com/huggingface/transformers/tree/master/utils) so that our maintenance isn't elevated by the high amount of duplicated code and so that our code coverage remains complete.
> 
> Thank you for your effort!

Right, got it. I'll close this PR and create another one keeping the changes you suggested in mind. Thanks!