``Target`` will be refactored down the road to support various
nuanced endpoint types. Thusly incorporating the scheduling
behavior within it will be problematic. To that end, the scheduling
behavior has been moved into a separate assistance type to improve
conciseness and testability.
``make format`` was also run.
``TargetPool`` is a pool of targets pending scraping. For now, it
uses the ``heap.Interface`` from ``container/heap`` to provide a
priority queue for the system to scrape from the next target.
It is my supposition that we'll use a model whereby we create a
``TargetPool`` for each scrape interval, into which ``Target``
instances are registered.
