Add stream command

[mattt]

$ replicate stream --help
Alias for "prediction create --stream"

Usage:
  replicate stream <owner/model[:version]> [input=value] ... [flags]

Flags:
  -h, --help                      help for stream
      --json                      Emit JSON
      --no-wait                   Don't wait for prediction to complete
      --output-directory string   Output directory, defaults to ./{prediction-id}
      --save                      Save prediction outputs to directory
      --separator string          Separator between input key and value (default "=")
      --stream                    Stream prediction output
  -w, --wait                      Wait for prediction to complete (default true)
      --web                       View on web

$ replicate stream meta/llama-2-70b-chat prompt="Tell me a joke about llamas"
Sure, here's a joke about llamas for you:

Why did the llama refuse to play poker?

Because he always got fleeced!

I hope that made you smile! Is there anything else I can assist you with?⏎