func (iter *Iterator) Previous() (ok bool) {
	if iter.didSeek {
		panic("not implemented")
	}
	return iter.inner.Previous()
}
Previous returns true if the iterator contains previous elements
and rewinds its state to the previous element if that is possible.
package goskipiter
import "github.com/ryszard/goskiplist/skiplist"
type Iterator struct {
	inner     skiplist.Iterator
	didSeek   bool
	seekWasOK bool
}
func New(inner skiplist.Iterator) *Iterator {
	return &Iterator{inner: inner}
}
func (iter *Iterator) Next() (ok bool) {
	if iter.didSeek {
		iter.didSeek = false
		return iter.seekWasOK
	} else {
		return iter.inner.Next()
	}
}