Previously, all `m.room.*` events were wodged into `{{room_events}}` which
isn't great when you want to pull specific ones out. Batesian had a 1:1
mapping of `render_foo()` to a section `{{foo}}`, and having to constantly
add functions for new types is a PITA. Batesian now supports returning a
`dict` instead of a section `string` where the keys are the `{{foo}}` and
the value is what will be inserted. Also add conflicting section key checks
to avoid multiple definitions of the same `{{foo}}`. Define dicts for
event schemata and swagger HTTP APIs.
Using this new feature, split out the instant messaging stuff from the events
section, and replace `{{room_events}}` with a list of specific events e.g.
`{{m_room_member_event}}`.
