Maintenance should also remove all downloaded files

[buresdv]

While brew cleanup removes caches, it does not remove the downloaded files.

Make a separate command to remove them, and maybe put it as an option in the maintenance sheet.

These files are located in /Users/david/Library/Caches/Homebrew/downloads. Don't forget to remove all the symlinks from /Users/david/Library/Caches/Homebrew! Otherwise these would be symlinks pointing to nowhere!