'Unregisters the given extension. No error is thrown if given extension isn\'t an extension or wasn\'t
registered yet.'

def unregister(self, extension):

    try:
        if issubclass(extension, PageExtension):
            self.page_extensions.remove(extension)
        elif issubclass(extension, TitleExtension):
            self.title_extensions.remove(extension)
    except KeyError:
        pass
