chore(php) Move to PHP 7

[Hywan]

Address hoaproject/Central#75.

[Pierozi]

Congrats, a major one! everything is moved to Source for better design where actual code base should be?
Should we apply this to every PHP7.1 PR?

[Hywan]

@Pierozi Yes. And yes :-).

This is WIP. It's very hard to test because hoa/test depends on libraries, which depends on hoa/test to test them… I've a weird local configuration. Hope I will close the loop soon, and we will iterate over other libraries more easily.