Select Reference Page - Make Join Syntax More Prominent

Hey,

Looking again at the SELECT Reference page while helping a novice user I
was once again annoyed but how the most common query syntax form for the
FROM clause is buried within a bunch of "how to generate a table" detail.

In this specific case I also was trying to describe why when you have three
tables to join that you can build a join tree and only actually use a
single from_item (IOW, no commas are required/allowed). From there it
became clear that from_item is serving two roles here and introducing a
structural element (join_expression) to represent the commonly used join
tree query form made sense. I then modelled the tree-like nature (using
the term recursive for now) explicitly as the left side of the join can be
either a new join_expression, extending the tree, or a from_item, bringing
the tree to its end.

In the description I had to move LATERAL up above all the join stuff since
it pertains to from_item and I wanted to call out the final set of
parameters as all being related to the join tree.

I'll do a pass at making sure we are using consistent terminology if this
has a shot of getting committed.

I've attached the patch and the resulting html page.

David J.