func (sb SortBy) Sort(trackers []*Tracker) {
	switch sb {
	case SortByMessage:
		sort.Sort(sortByMessage(trackers))
	case SortByMessageDsc:
		sort.Sort(sortByMessageDsc(trackers))
	case SortByPercent:
		sort.Sort(sortByPercent(trackers))
	case SortByPercentDsc:
		sort.Sort(sortByPercentDsc(trackers))
	case SortByValue:
		sort.Sort(sortByValue(trackers))
	case SortByValueDsc:
		sort.Sort(sortByValueDsc(trackers))
	default:
	}
}
Sort applies the sorting method defined by SortBy.
package progress
import "sort"
type SortBy int
const (
	SortByNone SortBy = iota
	SortByMessage
	SortByMessageDsc
	SortByPercent
	SortByPercentDsc
	SortByValue
	SortByValueDsc
)