Contribution: opcache_is_script_cached

Hello PHP documentation team, I've made my first PHP documentation contribution. There was a new opcache_is_script_cached() function added in PHP 5.6, but a proper documentation page was never added in the manual. I've made a first attempt at a basic page for the new function. I hope its sufficient, at least to start. The new patch can be found here: https://edit.php.net/?patchID=1458&project=PHP Please let me know if there's anything I did incorrectly. Thanks! - Trevor Suarez