cmd/main.go: add flag -cpuprofile to enable runtime/pprof profiling

cmd/main.go

@@ -7,8 +7,12 @@ import (
 	"os"
 	"bufio"
 	"io/ioutil"
+	"log"
+	"runtime/pprof"
 )
 
+var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
+
 func main() {
 	var b []byte
 
@@ -33,6 +37,15 @@ func main() {
 		Dlists: *optDlists,
 	}
 
+	if *cpuprofile != "" {
+		f, err := os.Create(*cpuprofile)
+		if err != nil {
+			log.Fatal(err)
+		}
+		pprof.StartCPUProfile(f)
+		defer pprof.StopCPUProfile()
+	}
+
 	doc := markdown.Parse(string(b), e)
 	w := bufio.NewWriter(os.Stdout)
 	doc.WriteHtml(w)