media-fonts/source-han-sans: lang select, updated config

Now, you can use USE="cn/jp/kr" to just use the select language
instead of downloading a full otc tarball. And you can use USE="otc"
if you want. You can't use otc and other languages at the same time
because the otc version included all languages.

And I just dropped the complex font substitute config and hint config,
and imported the config which fix some rendering issue.

Thanks Arch Linux.