Add fonts to preloading with integrity

this is currently not supported and is ignored but it does not hurt, it
speeds up the page load and as soon as it is supported in the future it
will start to work: https://crbug.com/981419

Signed-off-by: Knut Ahlers <knut@ahlers.me>

frontend/index.html

@@ -6,9 +6,20 @@
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 
+    {{ range (list "webfonts/fa-solid-900.woff2" "webfonts/fa-brands-400.woff2" "lato-v20-latin-ext_latin-regular.woff2" "lato-v20-latin-ext_latin-700.woff2") }}
     <link
+      as="font"
+      crossorigin="anonymous"
+      href="{{ . }}"
+      integrity="{{ assetSRI . }}"
+      rel="preload"
+    >
+    {{ end }}
+
+    <link
+      crossorigin="anonymous"
       href="css/all.min.css"
-      integrity="{{ SRIHash `css/all.min.css` }}"
+      integrity="{{ assetSRI `css/all.min.css` }}"
       rel="stylesheet"
     >
 
@@ -39,7 +50,8 @@
     <div id="app"></div>
 
     <script
-      integrity="{{ SRIHash `app.js` }}"
+      crossorigin="anonymous"
+      integrity="{{ assetSRI `app.js` }}"
       src="app.js"
     ></script>
   </body>

tplFuncs.go

@@ -11,7 +11,8 @@ import (
 var (
 	sriCacheStore = newSRICache()
 	tplFuncs      = template.FuncMap{
-		"SRIHash": assetSRIHash,
+		"list":     func(args ...string) []string { return args },
+		"assetSRI": assetSRIHash,
 	}
 )