Re: INSERT ... ON CONFLICT UPDATE/IGNORE 4.0

So I've committed the patch yesterday evening. I'm pretty sure there'll
be some more minor things to change. But overall I feel good about the
current state.

It'd be quite helpful if others could read the docs, specifically for
insert, and comment whether they're understandable. I've spent a fair
amount of time trying to make them somewhat simpler, but I do think I
only succeeded partially.  And there's also my own brand of english to
consider ;)

Phew.