[php-langspec][PR #234] - Define encoding of PHP scripts (Fix #233)

You can view the Pull Request on github:
https://github.com/php/php-langspec/pull/234

Comment by Agares:
I'll look into  fixing that during the weekend. And by the way I think your previous comment was referring to an older version of the merge request, as the current one uses the wording that @IMSoP proposed, which mentions ASCII only as the representation used in the specification, but defines characters as bytes. Please have another look and I'm happy to address any concerns if you still have them, let's make this as correct as possible.