Use nouse_stdio to avoid console.log pollution from destroying json response payload

[robotarmy]

Hello Mr Devinus,

I have used your library with some good effect in a proof of concept project at https://github.com/robotarmy/serve_elm.

I wonder if you would consider discussing these changes and perhaps exposing configuration for enabling other options for Port.open..

I use nouse_stdio to avoid console.log statements from becoming part of the output from your wrapper script.

I think their could be some cause for exposing the working directory option for the command to Port.open and also perhaps the ENV option.

Any thoughts?!

Thank you for your great work!