Merge branch 'develop' into markjh/synchrotronII

synapse/config/emailconfig.py

synapse/handlers/typing.py

synapse/metrics/__init__.py

synapse/metrics/metric.py

synapse/push/mailer.py

synapse/storage/__init__.py

synapse/storage/client_ips.py

synapse/util/async.py

synapse/util/caches/__init__.py

synapse/util/caches/descriptors.py

synapse/util/caches/dictionary_cache.py

synapse/util/caches/expiringcache.py

synapse/util/caches/stream_change_cache.py

tests/metrics/test_metric.py