Merge pull request #5102 from taosdata/hotfix/sangshuduo/TD-2901-csharp-taosdemo-with-mono-doesnot-exit

[TD-2901] <fix>: fix bug taosdemo with mono compiled does not exit.

Fix taosdemoTest2.py failure

[TD-2555]<test>add test for stddev

[TD-2493]<test>fix email error

[TD-2927]

[TD-2927]<fix>: fix the bug found in the regression test.

Feature/mac

[TD-2923]<fix>: Not show databases in dropping

[TD-2875]<fix>: comment out stderr print to make crash_gen no Killed

[TD-2882]<test>if core,stop test

[TD-1976]optimize read rows from cache

fix mem leak

[TD-2854]alter table with quoted table name failed

[TD-2885]fix memleak issue

[TD-2918]<fix>: delete stable in mnode first before send dnode drop st…

[TD-2875]<fix>: remove WINDOWS macro related code in ttimer

[TD-2555]<test>add test case for stddev

[TD-2419]<feature>save server info to file

[TD-2914] fix broken python2 connector by mistake adding threading mo…

[TD-2920] <doc>: nodejs connector update for 2.0.6.