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

cmd/qrbill-api/api.go

@@ -27,7 +27,6 @@ import (
 	"os"
 	"strings"
 
-	"github.com/davecgh/go-spew/spew"
 	"github.com/mattn/go-isatty"
 	"github.com/stapelberg/qrbill"
 
@@ -184,7 +183,7 @@ func logic() error {
 
 		case "txt":
 			w.Header().Add("Content-Type", "text/plain; charset=utf-8")
-			spew.Fdump(w, qrch.Validate())
+			fmt.Fprintf(w, "%s", bill.EncodeToString())
 
 		case "html":
 			debugHTML(w, r, prefix, qrch)

cmd/qrbill-api/api_gokrazy.go

@@ -1,3 +1,4 @@
+//go:build gokrazy
 // +build gokrazy
 
 // Copyright 2020 Google LLC

qrbill.go

@@ -263,6 +263,10 @@ type Bill struct {
 	qrcontents string
 }
 
+func (b *Bill) EncodeToString() string {
+	return b.qrcontents
+}
+
 func (b *Bill) EncodeToSVG() ([]byte, error) {
 	var err error
 	code, err := encoder.Encoder_encode(b.qrcontents, decoder.ErrorCorrectionLevel_M, qrEncodeHints())

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