Soft-reserve "void" class name

Hi internals! For PHP 7 we soft-reserved a number of class names [1] like "numeric", so that we have the ability to introduce them as typehints in a 7.x release. "Soft" here means that we only document these names as being reserved and don't throw an error when they're used. I'd like to add "void" to this list, so we have the option to introduce a void return type in PHP 7.x. I've seen some disagreement as to whether this should be called "void" or "null" - this discussion should be held when an RFC comes up, however we need to keep both options open until then. (Currently only "null" is reserved.) If people think that this requires a vote, I'll open one. Thanks, Nikita [1] https://wiki.php.net/rfc/reserve_even_more_types_in_php_7