Add Content-Length and Last-Modified headers to downloads

- Closes: #47

lib/trantor.go

@@ -1,6 +1,8 @@
 package trantor
 
 import (
+	"time"
+
 	log "github.com/cihub/seelog"
 
 	"fmt"
@@ -116,6 +118,8 @@ func downloadHandler(h handler) {
 	headers := h.w.Header()
 	headers["Content-Type"] = []string{"application/epub+zip"}
 	headers["Content-Disposition"] = []string{"attachment; filename=\"" + book.Title + ".epub\""}
+	headers["Content-Length"] = []string{fmt.Sprint(book.FileSize)}
+	headers["Last-Modified"] = []string{fmt.Sprint(book.UploadDate.Format(time.RFC1123))}
 	addCacheControlHeader(h.w, false)
 
 	io.Copy(h.w, f)