Support streaming speech API

[MarkEdmondson1234]

Its a good long wait in the Shiny app at the moment, as the API is more suited to batch calls. For true babel fish goodness, streaming API is needed, but that is only supported via "rpc" https://cloud.google.com/speech/docs/streaming-recognize

Some possibilities for supporting that are:

• gRPC https://github.com/nfultz/grpc/issues/12
• rprotobuf https://github.com/eddelbuettel/rprotobuf
• Wrapping python: https://cloud.google.com/speech/docs/streaming-recognize#speech-streaming-recognize-python

[MarkEdmondson1234]

I have no idea how to get started at this, so any help with examples of how it could work appreciated.