As part of jvt.me#409, we want to selectively syndicate to external
sites less often than originally thought, only adding the metadata if
required. This means that the content will be marked up with an array of
sites and their link text to be shown.

Also, don't even show the `#syndication-targets` container unless we're
actually syndicating, so HTML-Proofer knows when to complain about links
not being set.