use arrow to serialize requests to command line application / web framework

[cpritcha]

Right now the FuncRequest struct is being used. This has a number of draw backs:

• have to copy data between rust and host language or use language specific ffi APIs to provide a view of the data. Using language specific implementation information is costly in terms of development effort, copying data is fine for small struct is fine but it would be great to have the ability to pass Arrow record batches, tensors, json etc.
• restricted implementations of resources to rust. It would be useful if users could create their own resource types without having to extend meillionen or write a rust extension. Since arrow has many language bindings the host language can process arrow record batch and dispatch to appropriate resource handlers (that could be written in rust, python, r, java, julia etc) to load and save data

The arrow request should have a sink struct column and a source struct column. The sink struct column will have one column for every sink declared in the interface. The source struct column will have one column for every source declared in the interface. This will also issuing multiple run instructions to one cli program which will be useful later.

[cpritcha]

We also should have a consistent way of dealing with resource versioning so that they can be handled by models in a consistent way.

[cpritcha]

we use flatbuffers now