a mysql proxy support distributed transaction

todo list:

1. transaction optimize
2. node pool

3. optimize: rpc version server / rpc cli pool
4. optimize: log
5. benchmark
6. xa trx test (zz)
7. sharding support (hash, range date)

8. sql sharding support (where = , etc...)
9. prepare support
10. fix bug: mysql version gen
    --- after performance benchmark, will not use this place

11. rpc version server, add map[sessionid]map[uint64]byte
    --- reduce lock use .. need benchmark


12. 输入 流必须读取完？？
13. where shard support

14. exec plan
    1. exec plan's shard list for every layer
15. a join b where a.id = b.id and ... || or ... || in ... || ... support
    1. if select from (select * from tb) as t1 join (select * frm tt) as t2 on t1.id = t2.id; need to judge t1.shard == t2.shard

16. join & multi table plan support
17. plan.hide attr support


18. 统一 must rollback 处理
19. 整理 err
    - mysqlErr
    - 内部逻辑 err
20. handle audit

2018.7.11
21. binlog 回滚
22. prepare sql exec router test
23. backend conn pool

9.20
24. refactor prepare proto

9.29
25. add extra port which used to handle admin cmd