Merge pull request ruby#323 from yui-knk/plain_object_type

Make Type to be plain object

lib/lrama/grammar/type.rb

@@ -1,6 +1,18 @@
 module Lrama
   class Grammar
-    class Type < Struct.new(:id, :tag, keyword_init: true)
+    class Type
+      attr_reader :id, :tag
+
+      def initialize(id:, tag:)
+        @id = id
+        @tag = tag
+      end
+
+      def ==(other)
+        self.class == other.class &&
+        self.id == other.id &&
+        self.tag == other.tag
+      end
     end
   end
 end