Hackage shows non-public, internal libraries

[phadej]

This is wrong, please don't.

• https://hackage.haskell.org/package/puresat
• https://hackage.haskell.org/package/haskell-ci
• https://hackage.haskell.org/package/attoparsec

[nikita-volkov]

I second that and want to expand. There seems to be two problems currently.

1. If the visibility setting is not specified for an internal library, the docs for it are rendered as if it's public. However the Cabal docs state that internal libraries are private by default. See "attoparsec" for example.

2. If visibility is explicitly set to private the docs don't get rendered, but the contents of the internal library still get listed at the landing page of the package. See "hasql" for example.

I believe that in both cases Hackage should just ignore the internal packages and neither list or generate docs for them.

[gbaz]

This feature was introduced by @414owen in #1279 -- maybe they'd be open to a followup PR? Patches from others also welcome.