astropy/astropy — pull request #2691 by taldcroft (2014-07-04 15:33:28+00:00)
Title: Make representations sub-classable and demonstrate with Wrap180 test

This should partly address #2690 by making it convenient to subclass representations, and in particular change the `attr_classes` only. In the currently implementation the `attr_classes` are not actually used in the class but instead are hardwired.

It also provides a new test that serves as a demonstration of how to make a new frame and representation to accomplish some specific behavior.