add brew-cask formula to root

this is an attempt to make this repository `brew tap`able

brew-cask.rb

@@ -0,0 +1,37 @@
+require 'formula'
+
+class BrewCask < Formula
+  homepage 'https://github.com/phinze/brew-cask/'
+  head 'https://github.com/phinze/brew-cask.git'
+
+  skip_clean :all
+
+  def install
+
+    prefix.install_p 'lib', 'rubylib'
+    inreplace 'bin/brew-cask.rb', '/lib', '/rubylib'
+
+    prefix.install 'Casks', 'bin'
+    (bin+'brew-cask.rb').chmod 0755
+
+    unless cask_symlink_dst.symlink?
+      File.symlink(cask_symlink_src, cask_symlink_dst)
+    end
+  end
+
+  def cask_symlink_src
+    prefix+'Casks'
+  end
+
+  def cask_symlink_dst
+    HOMEBREW_PREFIX.join('Library','Casks')
+  end
+
+  def caveats; <<-EOS.undent
+    This formula installs a symlink that it cannot remove:
+      #{cask_symlink_dst} -> #{cask_symlink_src}
+    
+    You'll need to remove it manually if you want to uninstall.
+    EOS
+  end
+end