Faiss 1.5.3

Bugfixes:

• slow scanning of inverted lists (#836).

Features:

• add basic support for 6 new metrics in CPU IndexFlat and IndexHNSW (#848);
• add support for IndexIDMap/IndexIDMap2 with binary indexes (#780).

Misc:

• throw python exception for OOM (#758);
• make DistanceComputer available for all random access indexes;
• gradually moving from long to int64_t for portability.