CAB containers

~~This PR contains a major change - it adds a dependency to brew-cask itself.~~
Therefore I assume this PR needs some discussion and may not be accepted.
The added dependency is "cabextract", available through the homebrew
ecosystem.  The gain is the ability to install CAB archives.  CABs are
typically Windows-specific.  However, there will be another commit in this
branch showing an example of when installing a CAB in OS X might be useful.