Move all the caches into their own package, synapse.util.caches

synapse/federation/federation_client.py

synapse/state.py

synapse/storage/_base.py

synapse/storage/directory.py

synapse/storage/event_federation.py

synapse/storage/keys.py

synapse/storage/presence.py

synapse/storage/push_rule.py

synapse/storage/receipts.py

synapse/storage/registration.py

synapse/storage/room.py

synapse/storage/roommember.py

synapse/storage/state.py

synapse/storage/stream.py

synapse/storage/transactions.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/lrucache.py