Postgres Permissions Article

Hi All,

I wrote a blog post about the Postgres permissions system, and I thought
I'd share:

http://illuminatedcomputing.com/posts/2017/03/postgres-permissions/

The main point I wanted to convey, which I somehow never grasped
confidently from reading the docs or other articles, is how permissions
are purely additive. Also I wanted to gather in one place how to *see
the current permissions*, which seems to be missing/incomplete in many
other articles. Anyway, maybe it will be helpful for some of you! Or for
the true experts, if you see any errors, I'd be happy to know so I can
correct them.

I also shared a few opinions amidst the facts (like that `USAGE` for
schemas doesn't add much), so I am very pleased to have those
challenged. You can consider them my own outstanding questions. I'd be
especially grateful for any feedback there.

Yours,
Paul