Improve support for Tuples

[mmatczuk]

We should be able to scan and bind arrays and slices.

At the moment

func datatypesTuplesSimple(t *testing.T, session gocqlx.Session) {
	err := session.ExecStmt(`CREATE KEYSPACE IF NOT EXISTS examples WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 1}`)
	if err != nil {
		t.Fatal("create keyspace:", err)
	}

	err = session.ExecStmt(`CREATE TABLE IF NOT EXISTS examples.tuples(k int PRIMARY KEY, c tuple<int,int>)`)
	if err != nil {
		t.Fatal("create table:", err)
	}

	coordinates1 := [2]int{12, 34}
	coordinates2 := [2]int{56, 78}

	insert := session.Query(qb.Insert("examples.tuples").Columns("k").TupleColumn("c", 2).ToCql())
	insert.BindMap(qb.M{
		"k":   1,
		"c_0": coordinates1[0],
		"c_1": coordinates1[1],
	})
	if err := insert.Exec(); err != nil {
		t.Fatal("Exec() failed:", err)
	}
	insert.BindMap(qb.M{
		"k":   2,
		"c_0": coordinates2[0],
		"c_1": coordinates2[1],
	})
	if err := insert.Exec(); err != nil {
		t.Fatal("Exec() failed:", err)
	}

	row := &struct {
		K  int
		C [2]int
		C0 int `db:"c[0]"`
		C1 int `db:"c[1]"`
	}{}

	q := session.Query(qb.Select("examples.tuples").Columns("k", "c").ToCql())
	if err := q.Get(row); err != nil {
		t.Fatal(err)
	}
	t.Log(row)
}

At the moment it fails with gocql: not enough columns to scan into: have 2 want 3