func NewHash(s string) Hash {
	b, _ := hex.DecodeString(s)
	var h Hash
	copy(h[:], b)
	return h
}
NewHash return a new Hash from a hexadecimal hash representation
package plumbing
import (
	"bytes"
	"crypto/sha1"
	"encoding/hex"
	"hash"
	"sort"
	"strconv"
)
type Hash [20]byte
var ZeroHash Hash
func ComputeHash(t ObjectType, content []byte) Hash {
	h := NewHasher(t, int64(len(content)))
	h.Write(content)
	return h.Sum()
}