Generate FlowType definitions

[vjpr]

Would be cool to have FlowType definitions generated as well as the TypeScript defs.

[dcodeIO]

Would be cool, yeah, but that's nothing I'd spend time on because I use TS exclusively.

For reference, this is what's used for TS:
https://github.com/dcodeIO/protobuf.js/tree/master/cli/lib/tsd-jsdoc

The CLI utility could be named pbflow or something.

[stereobooster]

• protobuf2flowtype
• protobuf-js-typer
• protoc-gen-flow

See also gRPC to Flow

[vjpr]

I tried flowgen which converts d.ts to flow.js. Conversion works okay. But I think I will modify flowgen just to extract the types instead of the protobufjs classes...or just convert the protobufjs json output to flow types.