slices.go
func (s StringSlice) ExistsAllIgnoreCase(str []string) bool {
	for _, v := range str {
		if !s.ExistsIgnoreCase(v) {
			return false
		}
	}

	return true
}
func (s StringSlice) ExistsAllIgnoreCase(str []string) bool {
	for _, v := range str {
		if !s.ExistsIgnoreCase(v) {
			return false
		}
	}

	return true
}
//ExistsAllIgnoreCase determine whether all specified strings exists into
// current slice (ignores letter casing).