Currently the HTTP handlers are attached to an API mux which is created inside
Setup(). In the future, we'll want to split this out so a single mux can have
both sync and clientapi handlers attached to it.
This involves:
- Parsing the HTTP request
- Requesting auth events from the roomserver via the Query API
- Building the event
- Doing auth checks on the event
- Sending it to the roomserver input log
