add Module#{attr,attr_reader,attr_writer,attr_accessor}; close #257

mrblib/class.rb

+class Module
+  # 15.2.2.4.13
+  def attr_reader(*names)
+    names.each{|name|
+      define_method(name){self.instance_variable_get(name)}
+    }
+  end
+  # 15.2.2.4.14
+  def attr_writer(*names)
+    names.each{|name|
+      aset = (name.to_s+"=").intern
+      define_method(aset){|v|self.instance_variable_set(name,v)}
+    }
+  end
+  # 15.2.2.4.12
+  def attr_accessor(*names)
+    attr_reader(*names)
+    attr_writer(*names)
+  end
+  # 15.2.2.4.11
+  def attr(name)
+    attr_reader(name)
+  end
+end