cd and ls should treat zip files like directories

[LadyCailin]

It would be exceedingly nice to be able to just ls and cd into a zip file as if it were a directory. The core code already has support for this, so it should be generally easy enough to be able to add this in here. Changes would also probably need to be made to pwd and perhaps other functions that use the current working directory, so a survey should be done first to assess the impact here.