Merge pull request #37 from matrix-org/client_v2_filter

synapse/api/filtering.py

synapse/rest/client/v2_alpha/__init__.py

synapse/rest/client/v2_alpha/filter.py

synapse/server.py

synapse/storage/__init__.py

synapse/storage/filtering.py

synapse/storage/schema/delta/v13.sql

synapse/storage/schema/filtering.sql

tests/api/test_filtering.py

tests/rest/client/v2_alpha/__init__.py

tests/rest/client/v2_alpha/test_filter.py