Use partialCached to avoid any perf penalty.
TODO: limit the scope I pass to them.
I noticed a teeny tiny perf improvement after doing this, probably
because now some giant data structures only need to be generated once.
Add a new "Interactions" section to my pages that contain both
Syndication and Webmentions. Make the Syndication links u-syndication.
Make both these things children of the <article> h-entry.
