[feature] TTL on keys

[judahrand]

Would you be interested in an implementation on time to live (TTL) on keys in the data store? Redis for example has this functionality and it is probably sensible to use it to avoid a build up of redundant key, value pairs being kept.

Perhaps something similar to the throttled project in Go?

Again this is something I'm happy to put in a PR for if you're likely to review and accept it.

[sigmavirus24]

I considered implementing this from the start but didn't need it personally