Multiple php versions build matrix


Would be good feature if we can make build matrix for different php versions at once.

- 5.2
- 5.6
- nightly # PHP 7.0
- hhvm

In result it will try to make build with different php versions.

Partially related to: Build matrix #584


I gave some details on how can this be achieved for Python in this post. You should be able to adapt that to PHP by replacing pyenv with phpenv—we use that to manage the PHP environments.