func NewEmptyPrependableFromView(v View) Prependable {
	return Prependable{buf: v, usedIdx: len(v)}
}
NewEmptyPrependableFromView creates a new prependable buffer from a View.
package buffer
type Prependable struct {
	buf View
	usedIdx int
}
func NewPrependable(size int) Prependable {
	return Prependable{buf: NewView(size), usedIdx: size}
}
func NewPrependableFromView(v View) Prependable {
	return Prependable{buf: v, usedIdx: 0}
}