Merge pull request #1683 from Tencent/dev

for v2.4.2

update change log date

Merge pull request #1673 from Tencent/dev

for v2.4.1

Merge pull request #1652 from Tencent/hotfix_cpp_handler

update C++ demo code with MMKVHandler

migrate to Central Publisher Portal

Merge pull request #1609 from Tencent/dev

for v2.3.0

Merge pull request #1590 from Tencent/dev

for v2.2.4

Merge pull request #1576 from Tencent/dev

for flutter 2.2.3

tidy