References Linked
Quick edit to make references to issues into links.

The other docs just use the trailing underscores e.g. GH220_ 

I've just used this convention.
 Sorry if I'm not being clear - unless I'm missing something, you've only used the pointer "GH220_", but not the necessary link that the pointer "GH220" deferences.  If you look at another whatsnew.rst, you should see what I mean (at the bottom of the file are the full hyperlinks that get will get dereferenced by the sphinx parser)
