Add array variables extraction + injection around Mustermann expand method

[inouire]

Trying to fix #303

It's a bit tricky to handle array query variables as Mustermann handled expansion by itself.

We have to extract array variables of its scope otherwise it will choke on non-array variables

We can add serialized arrays afterwards so that Mustermann is not aware of them

[inouire]

Or maybe would it be Mustermann responsibility to do it in the expand function?

[inouire]

@timriley do you think it can be part of next release? Thanks

[timriley]

@inouire thank you for the nudge! Yes, this will absolutely be going in. I'll make sure I review it soon. We'll have a 3.0 rc coming out in a few weeks, and this will be included.