add "event" to Post Type Algorithm per publishing evidence

[tantek]

According to view source verification as of today, 8 of 9 online real world event post examples on different sites (each a different implementation) as documented here https://indieweb.org/event#IndieWeb_Examples (all but snarfed(hand coded markup inside WordPress) use h-event as the root object instead of h-entry (thanks to @gRegorLove verifying markup)

This is well beyond the methodology threshold of three independent verified publishing implementations, and thus sufficient to add "event" as an explicit post type based on detecting a top level "h-event" object.

As creating an event takes much more cognitive load (specifying name/summary, time, location typically at a minimum), directly relating to richer content (and responses), it makes sense to put event detection near the top or even first.

[tantek]

This issue is dependent on microformats/h-event#1 being resolved first

[tantek]

Since this spec is becoming a NOTE at W3C, it is longer dependent on microformats/h-event#1 being resolved first.

Remainder of issue was resolved by the commit to resolve #19