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.
- We don't want autocomplete on the webmention form, since users should
not be entering a link multiple times.
- Not all browsers support the "required" HTML5 attribute, so add the
"aria-required" HTML attribute too.
The site now has polygot markup and can handle both XHTML5 and HTML5
parsing rules. My staging site will be XHTML but my main site will be
HTML5, just in case of parse errors.
If other tools (e.g. LightHouse) end up supporting XHTML5, I'll consider
switching the content-type to XHTML.
