WIP: recipe to configure Zend Opcache for PHP 5.5
Enhancement: add zend_extension option so the extension is used/loaded
Enhancement: add a default recipe to install the package
Enhancement: Feels like cheating! ;)

 * up the memory limit (this is twice the size of our main code-base)
 * up "accelerated files" to cache more files
 * disable cli opcode cache
 * disable timestamp checking (we 'reload' on deploys)
 * remove revalidate frequency (we 'reload' on deploys)
 * up max wasted percentage

To be tested (or looked at further):

 * file override
 * optimization level
 * sane combination of save_comments and load_comments (maybe app specific)
Merge pull request #117 from till/topics/php-opcache

WIP: recipe to configure Zend Opcache for PHP 5.5