I added yields when calling user_left_room, but they shouldn't matter on
the master process as they always return None anyway.

The intention here is to split the class into the bits that can be done
on workers and the bits that have to be done on the master.

In future there will also be a class that can be run on the worker,
which will delegate work to the master when necessary.

Make RoomMemberHandler functions private that can be

extra_users is actually a list of UserIDs

Refactor get_or_register_3pid_guest

RoomMembershipRestServlet doesn't handle /forget

Due to the order we register the REST handlers `/forget` was handled by
the correct handler.

Add Measure block for persist_events

Move property setting from ReplicationLayer to base classes

Split out edu/query registration to a separate class

This seems like a useful thing to measure.

Add transactional API to history purge

Make the purge request return quickly, and allow scripts to poll for updates.

Queuing up purges doesn't sound like a good thing.

Factor run_in_background out from preserve_fn

Add a metric which increments when a request is received

It's useful to know when there are peaks in incoming requests - which isn't
quite the same as there being peaks in outgoing responses, due to the time
taken to handle requests.

rephrase the OPTIONS and unrecognised request handling so that they look
similar to the common flow.

It annoys me that we create temporary function objects when there's really no
need for it. Let's factor the gubbins out of preserve_fn and start using it.

Fix race in sync when joining room

The race happens when the user joins a room at the same time as doing a
sync. We fetch the current token and then get the rooms the user is in.
If the join happens after the current token, but before we get the rooms
we end up sending down a partial room entry in the sync.

This is fixed by looking at the stream ordering of the membership
returned by get_rooms_for_user, and handling the case when that stream
ordering is after the current token.

use bcrypt.checkpw

Implement purge_history by timestamp

Remove ability for AS users to call /events and /sync