Add OutputFormat#close method. (#55)

---------

Co-authored-by: Postmodern <[email protected]>

lib/ronin/core/output_formats/output_format.rb

@@ -42,6 +42,16 @@ def <<(value)
           raise(NotImplementedError,"#{self.class}#<< was not implemented")
         end
 
+        #
+        # Optional place holder method for closing any output file(s).
+        #
+        # @since 0.3.0
+        #
+        # @abstract
+        #
+        def close
+        end
+
       end
     end
   end