textproc/zxing-cpp: Update to 2.2.1

Update COMMENT and especially pkg-descr to be a bit more informative as
to what this port actually does.

Update WWW and remove GH_ACCOUNT. Project now redirects to an account by
the same name as PORTNAME.

https://github.com/zxing-cpp/zxing-cpp/releases/tag/v2.2.1
https://github.com/zxing-cpp/zxing-cpp/releases/tag/v2.2.0