Php 5.3 compatibility

Function array dereferencing is a feature introduced in PHP 5.4 (Cf http://www.php.net/manual/en/migration54.new-features.php).
The sparse uses of this in the SiteExport code make the plugin unusable (breaks DokuWiki) on PHP 5.3 setups.
Yes, I know PHP 5.3 is close to end-of-life… But still…

Anyhow, I hope I didn't make anything silly reimplementing the code. If I did, please be indulgent & try to adress this compatibility concern as best as you can.