[BREAKING] Split-up css into sub-parts (#317)

* Move styles into 3 different locations
- core
- common
- hljs

* Load all stylesheets in proper order

layouts/partials/head.html

@@ -27,11 +27,18 @@
 <meta name="msvalidate.01" content="{{ .Site.Params.analytics.bing.SiteVerificationTag }}" />
 {{- end}}
 <!-- Styles -->
-{{- $common := (resources.Match "css/*.css") | resources.Concat "assets/css/common.css" }}
+{{- $theme_vars := (resources.Get "css/core/theme-vars.css") }}
+{{- $reset := (resources.Get "css/core/reset.css") }}
+{{- $media := (resources.Get "css/core/zmedia.css") }}
+{{- $hljs := (resources.Get "css/hljs/an-old-hope.min.css") }}
+{{- $common := (resources.Match "css/common/*.css") | resources.Concat "assets/css/common.css" }}
+
+{{- /* order is important */}}
+{{- $core := (slice $theme_vars $reset $common $hljs $media) | resources.Concat "assets/css/core.css" }}
 {{- $extended := (resources.Match "css/extended/*.css") | resources.Concat "assets/css/extended.css" }}
 {{- /*  bundle all required css  */}}
 {{- /*  Add extended css after theme style */ -}}
-{{- $stylesheet := (slice $common $extended) | resources.Concat "assets/css/stylesheet.css" | minify }}
+{{- $stylesheet := (slice $core $extended) | resources.Concat "assets/css/stylesheet.css" | minify }}
 
 {{- if not .Site.Params.assets.disableFingerprinting }}
 {{- $stylesheet := $stylesheet | fingerprint -}}