Add WordPress benchmark

[pronskiy]

It would be great to test on a default WordPress set-up in addition to the Symfony and Laravel demo apps.

[kocsismate]

Hi Roman,

Adding Wordpress to the benchmark suite was my plan initially. However, it was a PITA to set it up automatically, so I postponed it. My main problem with Wordpress is that it relies on a database connection, so I'm a bit worried that the benchmark result would primarily depend on the DB performance rather than the PHP execution time itself. Nevertheless, I can try setting Wordpress up in the close future.