Add XRegExp dependency

[Jaifroid]

As a result of #179, and following the example of @mossroy's initial attempt to fix that in commit https://github.com/kiwix/kiwix-js/commit/25c34b6f0f3098d4aed5a4337d07dc2349df0703, we could add the XRegExp library as a dependency. For now, all this would do is to avoid having to maintain the Unicode punctuation regex in util.js., but it could be useful more broadly in the future since it patches RegExp support to provide many modern utilities.