The Hugo internal Twitter and OpenGraph templates assume your post
images are in the static directory. This tries to look them up in
the page bundle first and falls back to the Hugo default behavior.
I had overridden Hugo's OpenGraph template to improve it, but those
changes have been upstreamed in Hugo 0.19. We can use theirs now.
See: https://github.com/spf13/hugo/pull/3073
.Site.LastChange is the date of the last modification on the entire
site, not necessarily on the node we're currently showing, such as
a taxonomy list.
Hugo's current handling of dates in the opengraph partial needs
nome work to be more correct—for example: the usage of published
and updated times. This comes verbatim from the Hugo source tree.
See: tpl/template_embedded.go
