add a few more changes to the 1.7.0 changelog

https://github.com/jashkenas/underscore/blob/1.7.0/index.html#L2552 https://github.com/jashkenas/underscore/blob/1.7.0/index.html#L2585 https://github.com/jashkenas/underscore/blob/1.7.0/index.html#L2591