Add Bleu score

[SkafteNicki]

🚀 Feature

Motivation

Add Blue score to future NLP package:

• class implementation can be taken from flash: https://github.com/PyTorchLightning/lightning-flash/blob/master/flash/text/seq2seq/translation/metric.py
• already have a functional version in https://github.com/PyTorchLightning/metrics/blob/master/torchmetrics/functional/nlp.py that just need to be move to a new file in functional/text/bleu.py (for consistency)

Pitch

Alternatives

Additional context

After merge to torchmetrics + official release the metric should be deprecated from flash + lightning-transformer.

[github-actions[bot]]

Hi! thanks for your contribution!, great first issue!

[karthikrangasai]

@SkafteNicki I would like to work on this issue.

I have moved the file functional/nlp.py to functional/text/blue.py. Where should I put the class implementation ??

[SkafteNicki]

Hi @karthikrangasai, Please put the class implementation in a new folder text inside a file called bleu

[karthikrangasai]

@SkafteNicki I have created a PR with the changes suggested.

I think tests and docs have to be updated, could you guide me on this ?