Bring up-to-date with latest matrix-sdk (5d46b35d)

[andybalaam]

In my quest to make method names consistent I first needed to reflect previous changes from matrix-sdk.

[richvdh]

There is a reference to UserIdentity in the documentation for OlmMachine.get_identity which will need an update.

LGTM otherwise.

[richvdh]

(if you converted that reference to be a proper {@link ...}, like some of the other docs, then this sort of nonsense would be caught by CI)