def def_method(object, method_name, filename=nil)
      m = object.is_a?(Module) ? :module_eval : :instance_eval
      object.__send__(m, "def #{method_name}; #{@src}; end", filename || @filename || '(erubis)')
    end
def def_method(object, method_name, filename=nil)
      m = object.is_a?(Module) ? :module_eval : :instance_eval
      object.__send__(m, "def #{method_name}; #{@src}; end", filename || @filename || '(erubis)')
    end
if object is an Class or Module then define instance method to it,
 else define singleton method to it.