Improving Google PageSpeed score

As per https://github.com/Automattic/wp-super-cache/issues/42, it would be great if WPSC handled some additional settings recommended by Google PageSpeed, including KeepAlive and Cache Control.

This is what I use (works with Apache and LiteSpeed):

``
`Header set Connection keep-alive`
``
``
`Header set Cache-Control "max-age=29030400"`
`Header append Cache-Control "public"`
``
``
`Header set Cache-Control "max-age=2592000"`
`Header append Cache-Control "proxy-revalidate"`
``

Start by reviewing how WP Super Cache handles generated web-server configuration and cached responses, then compare that behavior with the KeepAlive and Cache-Control snippets in the issue. Done means the requested settings are supported without breaking Apache or LiteSpeed caching behavior, with verification for the affected asset types.

Written by the indexing model from the issue text.