Dark Mode (#168)

* Implement toggle button

* Dark mode mixins

* Dark mode color design

* Disable dark mode for prints

* Initial dark mode design

* Fix light mode mixin

* Disable dark mode on print style

* Move dark mode color scheme below the default style to allow referencing

* Fix dropdown

* Fix device-based dark mode

* Dark mode index page design

* Responsive auxiliary nav with dark mode toggle

* Remove box shadow when on smaller displays

* Prevent default on toggle click

* Move attribution/licensing to README.md

* Fix header padding on index page

* Background color transition animation

* Remove margin on index when on mobile displays

* Remove neon border when on mobile

* Fix post-header margin on mobile

* Lighten card headers in dark mode

scss/print.scss

@@ -11,6 +11,8 @@ $font-brand: 'Sriracha', Geneva, monospace;
 $font-family-sans-serif: $font-primary;
 $font-family-base: $font-primary;
 
+$disable-dark-mode: true;
+
 $grid-breakpoints: (
   xs: 0,
   sm: 500px,
@@ -94,6 +96,7 @@ $header-full-height: 100px;
 @import "bootstrap/scss/utilities";
 // @import "bootstrap/scss/print";
 
+@import "./dark";  // Need to disable for print styles
 @import "./global";
 // @import "./header";
 @import "./footer";