When using the `creative_letters` option, warnings are emitted when matching

This is due to the extra non-capturing group with a plus outside of the different regexes for letters.

Removing the + and outer parens removes this problem and still matches against creative letters.

I've opened a PR to address this: https://github.com/chrisvfritz/language_filter/pull/10

Start by reviewing the creative_letters matching logic and the linked pull request #10, which addresses the warning behavior. Done means matching creative letters without emitting warnings, while preserving the existing matches.

Written by the indexing model from the issue text.