2020-08-13 Update + PostgreSQL 13 Beta 3 Release Announcement Draft

Hi,

Attached is a draft of the release announcement for the update release
on 2020-08-13, which also includes the release of PostgreSQL 13 Beta 3.
Reviews and feedback are welcome.

This is a fairly hefty release announcement as it includes notes both
about the update release and the beta. I tried to keep the notes about
Beta 3 focused on the significant changes, with a reference to the open
items page. If you believe I missed something that is significant,
please let me know.

Please be sure all feedback is delivered by 2020-08-12 AoE.

Thanks,

Jonathan