Re: clean up docs for v12

Find attached updated patches for v12 docs.

Note that Alvaro applied an early patch for log_statement_sample_rate, but
unfortunately I hadn't sent a v2 patch with additional change from myon, so
there's one remaining hunk included here.

If needed I can split up differently for review, or resend a couple on separate
threads, or resend inline.

Patches are currently optimized for review, but maybe should be squished into
one and/or reindented before merging.

Justin