Add "expired" status for Code queries

[pixelmachine]

The docs say that a code query can be made on the status of a code with the statuses 'live', 'pending', 'expired', 'disabled'.

However a code can't be pending and it doesn't look like the 'expired' status exists for codes, though they certainly can expire.

Secondly you can query a code based on it's expiry date but that's not mentioned in the docs.

Plugin version

2.7.3 (and 3)

[engram-design]

Looks like just a docs issue, which I've updated. There are no live, pending or expired statuses for Codes, just enabled or disabled.

[pixelmachine]

Would be good if there were an expired status for codes though, since that's a key feature of a code! Would allow you to retrieve all expired codes regardless of date.

[engram-design]

Sure, I'll switch this to a feature request for that!