Replace bash release helper scripts with Go progam

cmd/gorepomod/internal/gen/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"bufio"
+	"log"
+	"os"
+	"strings"
+)
+
+const (
+	inputFile  = "README.md"
+	outputFile = "usage.go"
+)
+
+// Convert README.md to a usage function.
+func main() {
+	inFile, err := os.Open(inputFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer inFile.Close()
+	scanner := bufio.NewScanner(inFile)
+
+	w := NewWriter(outputFile)
+	w.prLn("// Code generated by internal/gen/main.go; DO NOT EDIT.")
+	w.prLn("package main")
+	w.prLn("")
+	w.prLn("")
+	w.prLn("const (")
+	w.prLn("  usageMsg = `")
+
+	// Skip the first two lines.
+	scanner.Scan()
+	scanner.Scan()
+	for scanner.Scan() {
+		line := scanner.Text()
+		line = strings.Replace(line, "`", "'", -1)
+		line = strings.Replace(line, "\\[", "[", -1)
+		line = strings.Replace(line, "\\]", "]", -1)
+		w.prLn(line)
+	}
+	w.prLn("`")
+	w.prLn(")")
+	w.close()
+
+	if err := scanner.Err(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+type writer struct {
+	f *os.File
+}
+
+func NewWriter(n string) *writer {
+	f, err := os.Create(n)
+	if err != nil {
+		log.Fatalf("unable to create `%s`; %v", n, err)
+	}
+	return &writer{f: f}
+}
+
+func (w *writer) prLn(line string) {
+	_, err := w.f.WriteString(line + "\n")
+	if err != nil {
+		log.Printf("Trouble writing: %s", line)
+		log.Fatal(err)
+	}
+}
+
+func (w *writer) close() {
+	if err := w.f.Close(); err != nil {
+		log.Fatal(err)
+	}
+}