Add Max-Hours and Max-Seconds

Better will be to avoid copy-paste here and to use not headers for params, but url's params, like:
`curl --upload-file ./hello.txt https://transfer.sh/hello.txt?max-downloads=5`

server/handlers.go

@@ -319,6 +319,18 @@ func MetadataForRequest(contentType string, r *http.Request) Metadata {
 		metadata.MaxDate = time.Now().Add(time.Hour * 24 * time.Duration(v))
 	}
 
+	if v := r.Header.Get("Max-Hours"); v == "" {
+	} else if v, err := strconv.Atoi(v); err != nil {
+	} else {
+		metadata.MaxDate = time.Now().Add(time.Hour * time.Duration(v))
+	}
+
+	if v := r.Header.Get("Max-Seconds"); v == "" {
+	} else if v, err := strconv.Atoi(v); err != nil {
+	} else {
+		metadata.MaxDate = time.Now().Add(time.Second * time.Duration(v))
+	}
+
 	return metadata
 }