add fonts in newer, better compressed formats

htdocs/css/openwebrx.css

@@ -322,7 +322,9 @@ input[type=range]:disabled {
 
 @font-face {
     font-family: 'roboto-mono';
-    src: url('../fonts/RobotoMono-Regular.ttf');
+    src: url('../fonts/RobotoMono-Regular.woff2') format('woff2'),
+         url('../fonts/RobotoMono-Regular.woff') format('woff'),
+         url('../fonts/RobotoMono-Regular.ttf') format('truetype');
     font-weight: normal;
     font-style: normal;
 }