docs: misc relnotes fixes

Here's a few changes for the relnotes.

There's a few related things going on:

1. First, we had some dead links, because we were linking to some non-built release notes (old ones were we didn't do RST yet). This was fixes by moving these old ones into the _static-directory.

2. Using the full titles makes most of these take up two lines in the toctree. The version number is really the only thing we should care about, though.

   This takes us from this:

   

   ...to this: