Allow adding additional css/js files (#52)

This allows adding css/js files in .Site.Params.css/js both relative or
aboslute to the site.
The resulting html inserts absolute paths only.

layouts/partials/css.html

@@ -13,10 +13,10 @@
 </style>
 
 <!-- main -->
-<link rel="stylesheet" href="{{ .Site.BaseURL }}/css/main.css">
+<link rel="stylesheet" href="{{ "css/main.css" | absURL }}">
 
 <!-- custom -->
-{{ range .Site.Params.css }} <link rel="stylesheet" href="{{ . }}"> {{ end }}
+{{ range .Site.Params.css }} <link rel="stylesheet" href="{{ . | absURL }}"> {{ end }}
 
 <!-- google fonts -->
 <link rel="stylesheet" href="https://fonts.googleapis.com/css?family={{ .Site.Params.font }}">

layouts/partials/js.html

@@ -10,7 +10,7 @@
 {{ end }}
 
 <!-- custom -->
-{{ range .Site.Params.js }} <script src="{{ . }}"></script> {{ end }}
+{{ range .Site.Params.js }} <script src="{{ . | absURL }}"></script> {{ end }}
 
 <!-- jquery -->
 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>