Add Sitesucker Cask

> SiteSucker is a Macintosh application that automatically downloads
> Web sites from the Internet. It does this by asynchronously
> copying the site's Web pages, images, backgrounds, movies, and
> other files to your local hard drive, duplicating the site's
> directory structure. Just enter a URL (Uniform Resource Locator),
> press return, and SiteSucker can download an entire Web site.
Merge pull request #942 from ohskylab/sitesucker

Add Sitesucker Cask