This package is responsible of sending checks to the execution pipeline with an interval specified for any number
of instance configurations coming along with any check. Only one Scheduler instance is supposed to run at any time
and even if this is not a requirement, a use case for multiple schedulers didn't show up and therefore wasn't tested.
A Scheduler instance keeps a collection of time.Tickers associated to a list of check.Checks: every time the
ticker fires, all the checks in that list are sent to the execution pipeline. Every queue runs in its own goroutine.
The Scheduler expose an interface based on methods attached to the struct but the implementation makes use of
channels to synchronize the queues and to talk with the scheduler loop to send commands like Run and Stop.
Once a scheduler is stopped, restarting it with Run is not expected to work. A new one should be instantiated and
Run instead.