Make staged_path work in installer stanzas

lib/hbc/dsl.rb

@@ -47,6 +47,10 @@ def sha256; self.class.sha256; end
 
   def artifacts; self.class.artifacts; end
 
+  def caskroom_path; self.class.caskroom_path; end
+
+  def staged_path; self.class.staged_path; end
+
   def caveats; self.class.caveats; end
 
   def accessibility_access; self.class.accessibility_access; end
@@ -217,6 +221,14 @@ def artifacts
       @artifacts ||= Hash.new { |hash, key| hash[key] = Set.new }
     end
 
+    def caskroom_path
+      @caskroom_path ||= self.caskroom
+    end
+
+    def staged_path
+      @staged_path ||= self.caskroom.join(self.name, self.version)
+    end
+
     def caveats(*string, &block)
       @caveats ||= []
       if block_given?