Adding REDIS support

[AndrewEastwood]

Also I added more options.

[gpspake]

Hey @AndrewEastwood
This looks great! Thanks for the PR.
I don't see any reason this can't be merged but I'd like to look through it a little more first.
We don't actually use Redis here so I'm not entirely familiar with your use case;
Could you share any details about how your using this or point me to some existing documentation?

[AndrewEastwood]

So if you switch to Redis and configure php to use redis as session storage then you can easily scale your app by adding nodes where each node will be looking into redis for active sessions :)

[gpspake]

Sorry I've been taking so long to get to this... the only concern that I have is that changes that have been made directly to PHPCAS. PHPCAS is a dependency of the project and is really only vendored in to the project for the sake of having it included in the wordpress.org plugin repository so it doesn't have to be built in when the plugin is installed.
Would it be possible to extract that stuff out of the PHPCAS directory so it's not hardcoded in if PHPCAS is updated?

[gpspake]

@AndrewEastwood just following up... Do you think it would be possible to extract these changes from PHPCAS as mentioned above? I'd love to be able to merge this in.
You might also consider submitting a PR directly to PHPCAS or creating a separate library that we could add to the project.

[AndrewEastwood]

@gpspake, yeah, I can transfer those change into a new PR for the PHPCAS. I just have a concern if they reject my changes then what will we do?

[AndrewEastwood]

Hey @gpspake! I moved all changes to the phpCAS repo. Let's wait for the @jfritschi's response.

[gpspake]

Awesome! good luck, let's hope it gets pulled. Worst case, they may at least provide an explanation for why they wouldn't merge it in. We've actually been discussing using Redis with CAS. Let's see what happens with that PR and go from there