[RFC] Language evolution (overview proposal)

Hi internals, I'd like to present an overview proposal on how to deal with opt-in backwards-incompatible changes: https://github.com/nikic/php-rfcs/blob/language-evolution/rfcs/0000-language-evolution.md This proposal is intended as a discussion starting point, so we can decide on the general direction we want to pursue. If we have a rough consensus, then a second proposal could sort out the details of a particular approach. A pull request is available to leave inline comments: https://github.com/php/php-rfcs/pull/2 Regards, Nikita