minizip: New package based on zlib derivation.

This is needed by Chromium and is part of the zlib source tree in
contrib/, so let's propagate the version of zlib and use the same source
tree.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
chromium: Build using minizip from nixpkgs.

Well, the gyp flag mentions "zlib" but in reality, minizip is used.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>