update version to 4.1.1.210903

Signed-off-by: itas109 <itas109@qq.com>

update LICENSE

Signed-off-by: itas109 <itas109@qq.com>

update CHANGELOG

Signed-off-by: itas109 <itas109@qq.com>

update README

update new release

update README.md

update VERSION

update CSerialPort 3.0.1.180214 Info

Add .gitignore

Add CSerialPort Demo