add sentence delimiter option to preserve original sentencization

[fsimonjetz]

Hi there,
it would be nice to have an option to preserve the original sentence boundaries by overriding the internal sentence splitter. The readme seems to imply that newlines will be used exclusively as sentence boundaries, but that is not the case. I added the option for my work, it might be useful for others as well but it should be revised by someone who is more familiar with the code.

Thank you!

[fbarrios]

Hi! Thank you for your contribution! We will review this in the following this.

[fbarrios]

Hi @fsimonjetz, looks good to me. I'm interested on knowing if you had a simple sample of a text that you wanted to summarize to maybe add it as a test.

Also, maybe this is clearer for the documentation?

Note that line breaks in the input will be used as sentence separators (along with punctuation), so be sure to preprocess your text accordingly. You can also provide a custom sentence delimiter through the sentence_delimiter argument.