txn.go
func (txn *Txn) SetWithMeta(key, val []byte, meta byte) error {
	e := &Entry{Key: key, Value: val, UserMeta: meta}
	return txn.SetEntry(e)
}
func (txn *Txn) SetWithMeta(key, val []byte, meta byte) error {
	e := &Entry{Key: key, Value: val, UserMeta: meta}
	return txn.SetEntry(e)
}
// SetWithMeta adds a key-value pair to the database, along with a metadata
// byte.
//
// This byte is stored alongside the key, and can be used as an aid to
// interpret the value or store other contextual bits corresponding to the
// key-value pair.
//
// The current transaction keeps a reference to the key and val byte slice
// arguments. Users must not modify key and val until the end of the transaction.