Breaking changes, rewrite; add support for plain text output and single page mode

assets/_markdown.scss

@@ -4,7 +4,7 @@
   line-height: 1.6;
 
   // remove padding at the beginning of page
-  > :first-child {
+  >:first-child, >section:first-child :first-child {
     margin-top: 0;
   }
 

assets/_shortcodes.scss

@@ -222,15 +222,6 @@
     margin: $padding-16 0;
   }
 
-  .book-hero {
-    min-height: $padding-16 * 24;
-    align-content: center;
-
-    h1 {
-      font-size: 3em;
-    }
-  }
-
   .book-codeblock-filename {
     background: var(--gray-100);
     border: $padding-1 solid var(--gray-200);

assets/icons/markdown.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="24px" viewBox="0 -960 960 960" width="24px" fill="#1f1f1f"><path d="M320-240h320v-80H320v80Zm0-160h320v-80H320v80ZM240-80q-33 0-56.5-23.5T160-160v-640q0-33 23.5-56.5T240-880h320l240 240v480q0 33-23.5 56.5T720-80H240Zm280-520v-200H240v640h480v-440H520ZM240-800v200-200 640-640Z"/></svg>