since most often, we need to get posts sorted in descending order by
date, we now just store the actual posts in a Vec, pre-sorted by date.
everything else that needs to reference posts now does so by the post's
index in that Vec.
pages are also changed to be stored/referenced in a similar manner, but
it is somewhat less important for pages since we don't do any real
enumeration of pages at all anywhere. but it's nice to be consistent.
posts can be specified with a date only, or date and time as desired.
it is up to the site's specific template to render posts with an
appropriate date/time format string based on what the author's
preferences
Gered