Go through the passed in list of attributes and register those renderers
        in the render map.

def _register_renderers(self, attrs):
        """
        Go through the passed in list of attributes and register those renderers
        in the render map.
        """
        for method in attrs:
            func = getattr(self, method)
            mimetypes = getattr(func, 'mimetypes', [])
            for mimetype in mimetypes:
                if not '/' in mimetype:
                    self.reject_map[mimetype] = func
                if mimetype not in self.render_map:
                    self.render_map[mimetype] = func
                else:
                    # about to redefine an already defined renderer.
                    # make sure this new render method is not on a base class.
                    base_classes = self.__class__.mro()[1:]
                    from_baseclass = any([x for x in base_classes if func.__name__ in dir(x)])
                    if not from_baseclass:
                        self.render_map[mimetype] = func