Implement a denser console output using unicode

[georgmu]

This is more or less a cross-issue I just posted in the qrcode-rust library project ( kennytm/qrcode-rust#39 ).

But since your project is more console-centric, maybe you are interested to add it in some form: https://gist.github.com/georgmu/eb37863f0bea3b8a1d18670587553e8a

[madprops]

This seems like something that would be implemented in qrcode-rust, and then just used here as an option.