resolve #379 audio classification evaluator + docs (#405)

* audio classification evaluator + docs

* fix styling issue

* [Docs] fixed a typo in bertscore readme (#386)

fixed typo in berscore readme

* Add max_length kwarg to docstring of Perplexity measurement (#411)

Added max_length kwarg to docstring of Perplexity measurement

* adding support raw audio input audio classification evaluator

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Co-authored-by: Hazrul Akmal <hazrulakmal121@gmail.com>
Co-authored-by: Kalyan Dutia <kalyan.dutia@gmail.com>