Versions/Editions are needed

[cmb69]

It is impossible to claim conformance to an ever evolving language specification without referring to a certain version/edition or whatever it will be called. There are open pull request and issues which cannot be sensibly addressed due to this issue, unless we're claiming this spec is still a draft, in which case it is not really helpful for alternative implementations at all.

[nikic]

In theory we have branches for specific versions, but in practice there is no bandwidth to maintain multiple versions of the specification. Langspec master targets current PHP master.