Get image data and/or put extra text with the image in the downlaod

[JanMisker]

I would like to offer the QR code for download but with some more context, e.g. instructions on where to scan it and for what purpose.

For this reason it would be useful if we can get a reference to the toDataURL() and toBlob() functions of the canvas. Then we can for example put it in a (client side) pdf or put it in another canvas that is then downloaded.

Another possibility could be to have to option to add text above and/or below the image in the download() call.

I'm more than willing to work on this feature myself, if more people want to use and test it.