feature: Save audio page wise or full book

[codeperfectplus]

Changelog

1. Now Users can Download Audiobooks as a page-wise or full book. Earlier it was only a saving page wise and the user need another library to merge all audio. It's fixed in this PR.
2. Docs Updated for the Save audio function

from audiobook import AudioBook
# argument: Speech-Speed="slow/normal/fast", volume = 0.0 to 1.0
ab = AudioBook(speed="normal", volume=1.0) 

# save_page_wise audio/whole book in one mp3 file
ab.save_audio(self, input_book_path, password=None, save_page_wise=False): 

@DrakeEntity Thanks to him for the suggestion.

[aayushi-droid]

useful for small books.

[aayushi-droid]

Merging the PR,