Grammar fix.
Queues are no longer Collections; this can be easily restored but after launch it is harder to strip this out. Renamed push to enqueue and pop to enqueue.
Stacks are no longer Collections.
Stacks and Queues have `isEmpty` again; was unintentionally lost when they stopped implementing Collection.
Moved `isEmpty` into a new interface `Ardent\Countable` and refactored to use it accordingly.
Fixed use statements.
Renamed Stack::peek to Stack::last.
Renamed Queue::peek to Queue::first.
Renamed findFirst and findLast to first and last respectively.
Misc naming convention updates.
Removed some unhelpful or easily inferred typehints; some spacing fixes too.