Add mechanism for handling binary data

[willcrichton]

We commonly have binary data, or data with sufficiently complex structure that it doesn't make sense to add it as SQL columns.

• Face features
• Face landmarks
• Poses
• Caption index

We should have a single consistent mechanism for creating, saving, loading (e.g. w/ mmap), searching, etc. packed binary files for each kind of data type.

[DanFu09]

See https://github.com/DanFu09/esper/blob/master/app/esper/pose_wrapper.py, https://github.com/DanFu09/esper/blob/master/app/esper/face_landmarks_wrapper.py, and https://github.com/scanner-research/esper/blob/master/app/esper/face_embeddings.py for some ad hoc solutions using https://github.com/scanner-research/rs-embed.