New feature: uppercase first letter in sentence, code cleanup

[ivoras]

Major change: making the first letter in the word following a "." or "?" uppercase (optional, defaults to off).
Minor changes: code cleanup, whitespace removal.

[oliverguhr]

Thanks for the PR! I always had the idea to add true casing to the model.

However, I see an issue here. For example, given the following text:

this is an test my name is oliver

the output would be:

this is an test. My name is oliver.

This true casing would only work after a "." or "?" not at the beginning of a sentence and not with "!" as we don't detect them.

[ivoras]

This true casing would only work after a "." or "?" not at the beginning of a sentence and not with "!" as we don't detect them.

I don't know what you mean with "!", as the patch doesn't use it, but I've also noticed it doesn't capitalise the starting sentence of the text, so I've updated the patch.

I know this is not proper true-casing as that would probably involve also applying it to possible names inside sentences, but it's good enough for my needs. There's a model on HF that attempts to do that (1-800-BAD-CODE/xlm-roberta_punctuation_fullstop_truecase) but it's too buggy.