404 not found performance improvements

benchmark            old ns/op     new ns/op     delta
Benchmark404         737           249           -66.21%
Benchmark404Many     2330          454           -80.52%

benchmark            old allocs     new allocs     delta
Benchmark404         3              0              -100.00%
Benchmark404Many     10             0              -100.00%

benchmark            old bytes     new bytes     delta
Benchmark404         115           68            -40.87%
Benchmark404Many     235           57            -75.74%

render/data.go

@@ -13,7 +13,7 @@ type Data struct {
 
 func (r Data) Write(w http.ResponseWriter) error {
 	if len(r.ContentType) > 0 {
-		w.Header().Set("Content-Type", r.ContentType)
+		w.Header()["Content-Type"] = []string{r.ContentType}
 	}
 	w.Write(r.Data)
 	return nil

render/text.go

@@ -6,6 +6,7 @@ package render
 
 import (
 	"fmt"
+	"io"
 	"net/http"
 )
 
@@ -24,7 +25,7 @@ func (r String) Write(w http.ResponseWriter) error {
 	if len(r.Data) > 0 {
 		fmt.Fprintf(w, r.Format, r.Data...)
 	} else {
-		w.Write([]byte(r.Format))
+		io.WriteString(w, r.Format)
 	}
 	return nil
 }