Basic server (`renkon serve`) w/ read + write access to dataframe store.

[DylanLukes]

Tentative plan: just use this off-the-shelf (already use Arrow IPC as standard format, and it is rapidly becoming a standard for other tools).

https://arrow.apache.org/docs/format/Flight.html https://arrow.apache.org/docs/python/generated/pyarrow.flight.FlightServerBase.html

Pros:

• "For free" interop with other tools.
• Don't need to write a protocol.
• gRPC already handles connection state, failure, etc.

Cons:

• Adds dependencies on gRPC and Protobufs.

[DylanLukes]

Instructive example:

https://arrow.apache.org/cookbook/py/flight.html

Renkon fits this very well, plus some actions for initiating and querying inferences.

[DylanLukes]

CLI for server and stub implementation (does nothing) implemented in #15.