= Expirable

Require the library.

  require 'mixers/expirable'

Example class.

  class X
    extend Expirable
  end

Now the experation can be set to a Time object, or a number of seconds
from +Time.now+. For instance, to set the expiration for one second
from now:

  X.expiration = 1

We can see the the object has not yet expired.

  X.refute.expired?

But if we wait one second.

  sleep 1

Then it will have expired.

  X.assert.expired?

Expiration does not invoke a trigger, it is merely queriable.