Add CLI progress bars to the packer tool

Since packing can be quite slow, it is nice to display progress to the
caller. We use the excellent github.com/vbauerster/mpb library to do so,
and add a bit of colour with github.com/logrusru/aurora.

Finally, augment the inspector and packer with a summary printer that
displays the overall file size/count, and compression ratio for each
compression type.

cmd/htpacker/inspector.go

@@ -32,7 +32,6 @@ var inspectCmd = &cobra.Command{
 
 // Inspect a packfile.
 //  TODO: verify etag; verify integrity of compressed data.
-//  TODO: skip Gzip/Brotli if not present; print ratio.
 func Inspect(filename string) error {
 	f, err := os.Open(filename)
 	if err != nil {
@@ -65,10 +64,46 @@ func Inspect(filename string) error {
 					printSize(info.Brotli.Length), info.Brotli.Offset)
 			}
 		}
+		inspectSummary(dir)
 	}
 	return err
 }
 
+func inspectSummary(dir *packed.Directory) {
+	var (
+		n, ngzip, nbrotli int
+		s, sgzip, sbrotli uint64
+	)
+
+	for _, f := range dir.Files {
+		n++
+		s += f.Uncompressed.Length
+		if f.Gzip != nil {
+			ngzip++
+			sgzip += f.Gzip.Length
+		}
+		if f.Brotli != nil {
+			nbrotli++
+			sbrotli += f.Brotli.Length
+		}
+	}
+
+	fmt.Printf("Uncompressed:\n\tFiles: %d\n\tSize:  %s\n",
+		n, printSize(s))
+	if ngzip > 0 {
+		fmt.Printf("gzip compressed:\n\tFiles: %d (%.1f%% of total)\n"+
+			"\tSize:  %s\n\tRatio: %.1f%%\n",
+			ngzip, 100*float64(ngzip)/float64(n),
+			printSize(sgzip), 100*float64(sgzip)/float64(s))
+	}
+	if nbrotli > 0 {
+		fmt.Printf("brotli compressed:\n\tFiles: %d (%.1f%% of total)\n"+
+			"\tSize:  %s\n\tRatio: %.1f%%\n",
+			nbrotli, 100*float64(nbrotli)/float64(n),
+			printSize(sbrotli), 100*float64(sbrotli)/float64(s))
+	}
+}
+
 func printSize(size uint64) string {
 	switch {
 	case size < 1<<10: