make format=txt display the textual QR code contents

This allows for easy comparison with QR codes extracted from PDFs:

pdfimages -png invoice.pdf invoice && \
  zbarimg --raw invoice*.png > code.txt

third_party/goembed/goembed.go

@@ -1,5 +1,6 @@
 // copied from https://github.com/dsymonds/goembed/ with pull requests applied
 
+//go:build ignore
 // +build ignore
 
 // goembed - Embed data in Go source code