Count records function

Please add count records function ;)

use SCARD redis command:
[https://redis.io/commands/scard](https://redis.io/commands/scard)


Examples:
```
redis>  SADD myset "Hello"
(integer) 1
redis>  SADD myset "World"
(integer) 1
redis>  SCARD myset
(integer) 2
```