1.5 CHANGES and Release Notes

Hi all.

We are making pretty good progress toward a 1.5 beta/release candidate,
so I decided to take a look at the release notes. I've attempted to
flesh out the parts that were lacking by using the relevant
documentation in notes/. However, some of those docs may be
out-of-date, or too technical for the intended audience of the release
notes. If the primary author(s) of each of the major features would
edit the relevant content for both length and clarity, I'd appreciate it.

As for CHANGES, I seem to recall someone (glasser?) mentioning in IRC
the other day that they would handle it. Could whoever-you-are please
step forward? ;)

Due to our fair protracted release process for 1.5, I don't think it
unreasonable to target CHANGES and the release notes to be finished by
the start of the release candidate phase. Let's set that as a target.

-Hyrum