Check against future dates

Future dates should evaluate to false for attribute and query methods,
such that an item with `expired_at == 1.day.from_now` is not `expired?`.
time_for_a_boolean 0.0.2

* Improve documentation in README.
* Add cheeky dialogue.
* Fix incorrect gem homepage.
* Dates in the future no longer evaluate to true, such that an item with
  `expired_at == 1.day.from_now` is not `expired?`.