“For better or worse, we are the Court of Appeals for the Hollywood Circuit. Millions of people toil in the shadow of the law we make, and much of their livelihood is made possible by the existence of intellectual property rights. But much of their livelihood - and much of the vibrancy of our culture - also depends on the existence of other intangible rights: The right to draw ideas from a rich and varied public domain, and the right to mock, for profit as well as fun, the cultural icons of our time.”