[Metrics] addition of wiki_split metrics
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#take
2021-07-07T11:09:12Z
https://github.com/huggingface/datasets/issues/2606#issuecomment-875514180
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2021-07-07T11:09:12Z
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**Is your feature request related to a problem? Please describe.**
While training the model on sentence split the task in English we require to evaluate the trained model on `Exact Match`, `SARI` and `BLEU` score
like this 
![image](https://user-images.githubusercontent.com/26653468/124746876-ff5a3380-df3e-11eb-9a01-4b48db7a6694.png)
While training we require metrics which can give all the output

Currently, we don't have an exact match for text normalized data

**Describe the solution you'd like**
A custom metrics for wiki_split that can calculate these three values and provide it in the form of a single dictionary
For exact match, we can refer to [this](https://github.com/huggingface/transformers/blob/master/src/transformers/data/metrics/squad_metrics.py) 

**Describe alternatives you've considered**
Two metrics are already present one more can be added for an exact match then we can run all three metrics in training script

#self-assign