def clear(task = :default)
      return nil unless tasks.keys.include?(task)
      stop task
      tasks[task][:history].clear
    end
def clear(task = :default)
      return nil unless tasks.keys.include?(task)
      stop task
      tasks[task][:history].clear
    end
Removes all history for a given task

 @param [Symbol] task The name of the task to clear history from.
 @return [NilClass] Returns nil