dark mode 😎 (#112)

* prepare dark mode stuffs

* themed all global colors

* store preference in local storage

* toggle styling

* lightbulb position

* minify bundled script with uglify-js instead of hugo

* detect whether user has an OS-wide dark mode preference and use that by default

* two different colors for each homepage link

* inline bulb SVGs into stylesheet

* fingerprint and cache styles for a year

* fix lightbulb positioning with weird magic numbers, will come back to that

* themed syntax highlighting

* use terser instead of uglify-js (b/c of ES6)

assets/sass/pages/_single.scss

@@ -7,12 +7,15 @@ main#single {
   margin: 0 auto;
 
   div#meta {
-    color: $color-medium;
     font-size: 0.85em;
     line-height: 1.3;
     letter-spacing: 0.04em;
     margin-top: 0.8em;
 
+    @include themed() {
+      color: t(color-medium);
+    }
+
     a {
       color: inherit;
     }
@@ -37,7 +40,10 @@ main#single {
   div#comments {
     margin-top: 1.5em;
     padding-top: 0.5em;
-    border-top: 2px solid $color-light;
+
+    @include themed() {
+      border-top: 2px solid t(color-light);
+    }
 
     div.utterances {
       max-width: unset;
@@ -45,7 +51,6 @@ main#single {
   }
 }
 
-
 // Responsive
 @mixin responsive--single() {
   main#single {