Write code for generating QR codes from string in pure Go using only standard library. I don't want a quick example, I want to actually implement each step in the process of generating a qr code image from arbitrary data like url strings.

Follow these steps: Proceed to implement encoding the data, then implement creating the qr matrix, then implement applying error correction, then implement placing the data.

The code must be valid and working! Provide output image if possible. Thank you!