Add interfaces to initialise session ID

[kynx]

This PR adds two interfaces:

• InitializeSessionIdInterface adds an initialiseId() method to sessions. This returns the session ID, creating a new ID if not present or regenerating an existing one
• InitializePersistenceIdInterface adds an initialiseId() method to persistence. This returns a new Session with the ID generated / regenerated if required.

LazySession can now initialise the ID if the persistence supports it.

I outlined a couple of use cases on the forum. Though when I wrote that I was thinking the session would also needed to be started. I've since realised that isn't required.

[boesing]

Wondering if @Ocramius https://github.com/psr7-sessions/storageless would be better for problems like yours.

Maybe you have a look on that project and re-think if you still need these changes in here.

[kynx]

Yeah, aware of that. Doesn’t really fit for the current project.

Curious though, given that you can getId() on an existing session, what’s the reason not to get the id of a new / regenerated one?

[weierophinney]

Thanks, @kynx — merged, and released with 1.3.0.