3.2.4

fix: Improve keep extension (#857)

* tests: add failing test case

* docs: add comment

* tests: add comment

* tests: add a test case that proves that the regex was always bad

* fix: replace regex with reliable filtering

* feat: stop at first invalid char

* feat: allow numbers in file extensions

* feat: stop extension from being '.'

* refactor: code style

* docs: use slugify in the example

* chore: prepare release