Support multi-read requests

[lzydmxy]

Which issues of this PR fixes:

This PR try to close #86

Change log:

• Support multi-read ops
• remove stat in simple-list response

[JackyWoo]

@lzydmxy please rebase the master into your branch.

[lzydmxy]

@lzydmxy please rebase the master into your branch.

okay~

[lzydmxy]

MuiltReadReponse for ClickHouse Keeper a little different from ZK.
In error handle, for example, get a node does not exist.
for ZK

MultiHeader(type=-1, done=False, err=-101), body='-101'

for ClickHouse Keeper

MultiHeader(type=8, done=False, err=-101)

Zk comes with an extra body (int) to indicate errors, error code is duplicated in header and in response body, and set ops_type to -1 for err.
But ClickHouse Keeper move body, and remain ops_type unchanged.

@JackyWoo Should we keeper zookeeper style, or change to ClickHouse Keeper?

[JackyWoo]

Can CK be compatible with the handling approach of ZK?

[lzydmxy]

Can CK be compatible with the handling approach of ZK?

Yes, CK is compatible with the handling approach of ZK. This is just an optional optimization.