demo: add an unprotect-xlsx demo that will unprotect an XLSX

This demo will remove both the workbook and individual sheet
protections.

cmd/unprotect-xlsx/main.go

@@ -0,0 +1,55 @@
+// Copyright 2017 Baliance. All rights reserved.
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"text/tabwriter"
+
+	"baliance.com/gooxml/spreadsheet"
+)
+
+func main() {
+	flag.Parse()
+	if flag.NArg() != 1 {
+		log.Fatalf("pass a single document as a parameter")
+	}
+	fn := flag.Arg(0)
+	fmt.Println("reading", fn)
+	wb, err := spreadsheet.Open(fn)
+	if err != nil {
+		log.Fatalf("error opening: %s", err)
+	}
+
+	prot := wb.Protection()
+	// just print out some info on what is protected
+	tw := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
+	if pwh := prot.PasswordHash(); pwh != "" {
+		fmt.Fprintf(tw, "password hash\t%v\n", pwh)
+	}
+	fmt.Fprintf(tw, "locked structure\t%v\n", prot.IsStructureLocked())
+	fmt.Fprintf(tw, "locked windows\t%v\n", prot.IsWindowLocked())
+	for _, s := range wb.Sheets() {
+		fmt.Fprintf(tw, "Sheet '%s'\n", s.Name())
+		sp := s.Protection()
+		if pwh := sp.PasswordHash(); pwh != "" {
+			fmt.Fprintf(tw, " - password hash\t%v\n", pwh)
+		}
+		fmt.Fprintf(tw, " - sheet locked\t%v\n", sp.IsSheetLocked())
+		fmt.Fprintf(tw, " - objects locked\t%v\n", sp.IsObjectLocked())
+
+		s.ClearProtection()
+	}
+	tw.Flush()
+
+	// then clear protection and resave the workbook
+	wb.ClearProtection()
+	op := strings.Replace(fn, filepath.Ext(fn), "-unprotected.xlsx", 1)
+	fmt.Println("saving unprotected workbook to", op)
+	wb.SaveToFile(op)
+}