sort.Interface sort by title, artist

sort.go

type byTitleArtist []*Track

func (t byTitleArtist) Len() int      { return len(t) }
func (t byTitleArtist) Swap(i, j int) { t[i], t[j] = t[j], t[i] }
func (t byTitleArtist) Less(i, j int) bool {
	if toL(t[i].Title) < toL(t[j].Title) {
		return true
	}
	if toL(t[i].Title) > toL(t[j].Title) {
		return false
	}
	return toL(t[i].Artist) < toL(t[j].Artist)
}