Support txn insert

[lsy3993]

Txn insert is the SQL which starts with 'BEGIN' and ends with 'COMMIT/ROLLBACK'. The general SQL may be like this :

begin;

// insert stmt
insert into table1 select xxx;
insert into table1 values();

// update stmt
update table1 SET xx where yy;
update table2 SET xx where yy;

// delete stmt
delete table3 where yy;

commit;

There are some tips should be mentioned:

1. you can only insert into one same table
2. the insert table must be different with the delete table

And this PR support insert stmt only, means SQL like:

begin;
insert into table1 select xxx;
insert into table1 values();
commit;

The delete and update stmt may support later.

[lsy3993]

new PR is : #234