HHVM FastCGI

Work in progress, opening PR for review. Seems to work though - kind of, maybe, sometimes, on my machine...

Branch is based on https://github.com/till/easybib-cookbooks/pull/344 because it depends on HHVM, obviously.

Still needs:
* [ ] deploy recipe (or maybe we can add that later)
* [ ] cleanup
* [ ] tests / chefspec / whatever (stolen from php-fpm recipe and commented-out currently)
* [ ] sanity testing re: config file locations / content
   * [ ] I think I'll need to add an init.d script to tell hhvm to use the `php-fcgi.ini` in server mode
   * [ ] most of the extensions configuration can probably go
   * [ ] memory limit may need to get increased