* QR code rendering for SHCs fixed for images - had to use
Nuintun QRcode lib and render in 2 chunks (byte and numeric),
was not possible to do this with zxing
* Add support for image file processing (Thanks upstream!)
* Added support for scanning all pages in a PDF for SHC codes
* Simplified ON receipt detection algorithm (well-known PDF info)
* Re-hide render canvas at bottom of page
* Minor README updates
* TBD: Handle multi-jurisdiction SHCs cleanly (not all data is being
properly passed along at the moment leading to missing card data)
* TBD: blow up if invalid issuer detected in SHC (currently allows
card creation even with invalid issuer)
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