Command syntax is now:
```
ZSCAN key cursor [MATCH pattern] [COUNT count] [NOSCORES]
```
Return format:
```
127.0.0.1:6379> zadd z 1 a 2 b 3 c
(integer) 3
127.0.0.1:6379> zscan z 0
1) "0"
2) 1) "a"
2) "1"
3) "b"
4) "2"
5) "c"
6) "3"
127.0.0.1:6379> zscan z 0 noscores
1) "0"
2) 1) "a"
2) "b"
3) "c"
```
when NOSCORES is on, the command will only return members in the zset,
without scores.
For client side parsing the command return, I believe it is fine as long
as the command is backwards compatible. The return structure are still
lists, what has changed is the content. And clients can tell the
difference by the subcommand they use.
Since `novalues` option of `HSCAN` is already accepted
(redis/redis#12765), I think similar thing can be done to `ZSCAN`.
---------
Signed-off-by: Chen Tianjie <TJ_Chen@outlook.com>
ba9dd7b23a