Might not be complete, needs check with current G Suite interfaces.
But improves on the current situation.

It can now be used with \SimpleSAML\Auth\Simple, although the old name still works too.

Also tweak wording of artifact idp docs a bit re memcache extension.

Minor format and exception message fixes, plus add information about the different communication channels we have today.

The guidelines on how to write your own module talk about the process() method receiving a “$request” or a “$state” parameter, instead of being consistent and sticking to just one of the names. Use “$request”.

`core:ScopeFromAttribute` is a generalised version of this.

Closes: #512

This should help people configure the PHP session handler and mitigate issues when sessions collide. Related to #478.