Make it easy to set emitter config for CLIs

[brendanzab]

It would be nice if we had a good way to set the styling for terminal CLIs in a standard way, without too much drama - either via command line flags or config files. I'm not sure what this would look like though, and I don't want to couple us to a specific command line parser or config format, but am also wary of something too astronautical.

Ultimately we should be able to set up the emitter example have its display configuration be customisable without too much trouble.

[brendanzab]

Chalk has a nice syntax for colors, eg. bold.rgb(10,100,200).