[BUGFIX] Use RecursiveRegexIterator with recursive regex

Bugfix for those using PHP5.4, where the `pages` variable is always an empty
array. This is because you have to use a recursive iterator when recursively
iterating through the directories/files.

In addition, the regex must also have a trailing `i`, indicating that it will
be used recursively.

Also see [this user note](http://php.net/manual/en/class.recursivedirectoryiterator.php#97228).

**Releases:** 1.3.0