Use static.danilafe.com to host KaTeX CSS/Fonts, and make that configurable.

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

config.toml

@@ -0,0 +1,2 @@
+[params]
+katexCssUrl = "https://static.danilafe.com/katex/katex.min.css"

layouts/partials/head.html

@@ -12,7 +12,7 @@
 
     <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Inconsolata:wght@400;700&family=Raleway&family=Lora&display=block" media="screen"> 
     <link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/normalize/5.0.0/normalize.min.css" media="screen">
-    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.2/dist/katex.min.css" integrity="sha384-bYdxxUwYipFNohQlHt0bjN/LCpueqWz13HufFEV1SUatKs1cm4L6fFgCi1jT643X" crossorigin="anonymous">
+    <link rel="stylesheet" href="{{ .Site.Params.katexCssUrl }}" crossorigin="anonymous">
     {{ range .AlternativeOutputFormats -}}
     <link rel="{{ .Rel }}" type="{{ .MediaType.Type | html }}" href="{{ .Permalink | safeURL }}">
     {{ end -}}