Allow resetting (clearing) of eVars with the JavaScript beacon

[#1]

At the moment, the expiry of eVars is very limited

1. If you have an event expiry eVar, it will persist across visits
2. You cannot reset an eVar with multiple events
3. You cannot clear the value of an eVar dynamically

Examples of why this is bad

1. If a visitor selects a product, and then lets their session time out, on the next visit they will be associated with that product even if your website does not remember them
2. If you have 2 ways of buying, one online (purchase event) and another reserving in store (referral event) then you cannot expire the products eVar with both, only one
3. If you have 2 (non-manditory) search boxes and perform a search in one, it will be persisted even if a user then goes on to perform a search with that search box empty

The fix

Allow us to reset an eVar in the JavaScript beacon. It could be as simple as setting

s.eVar1 = "~empty~"

Which would reset the eVar at that point. It could be done in the s_code or in the DOM

[#2]

I'm not sure doing this thru the JavaScript is the way to go but agree eVar expiry options need  to be made more flexible.

Ideally I'd like to see Adobe allow us to select multiple expiry options for each in the admin console.

[#3]

Yes we need a way to expire an eVar by more than one custom event. I want to use this for listvars so that I can measure impression/click events in a single listvar.