Applied perfsprint linter

- concatenate simple sprint calls
- use errors.New when possible
- use strconv for "%d" or "%x" sprint calls

tools/docs/main.go

@@ -20,6 +20,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"strconv"
 	"strings"
 
 	figure "github.com/mangoumbrella/goldmark-figure"
@@ -199,7 +200,7 @@ func getEtag(name string, src ...io.Reader) string {
 	if err != nil {
 		log.Fatal(err)
 	}
-	return fmt.Sprintf("%x", h.Sum64())
+	return strconv.FormatUint(h.Sum64(), 16)
 }
 
 func newManifest(fileList []*File) (*Manifest, error) {

tools/ftr/main.go

@@ -224,7 +224,7 @@ var lineRE = regexp.MustCompile(`^(.+?)(?:\((.+)\))?:\s*(.*)$`)
 
 func parseLine(line string) ([3]string, error) {
 	if !lineRE.MatchString(line) {
-		return [3]string{}, fmt.Errorf("Cannot parse line")
+		return [3]string{}, errors.New("Cannot parse line")
 	}
 
 	m := lineRE.FindAllStringSubmatch(line, -1)