Inspect, eql?, == and hash should work even when no attributes are specified

[louismrose]

The following code does not cause the inspect, eql?, == and hash methods to be added:

class Foo
  extend Attributable
end

For now, the workaround is to call attributes with no arguments:

class Foo
  extend Attributable
  attributes
end

But note that this highlights a slight bug in inspect:

Foo.new.inspect => "<Foo >"