Preserve whitespace in src blocks.

default_environment/stylesheet/main.css

@@ -76,6 +76,10 @@ body {
 
         .src_body {
             margin: 0.5rem;
+
+            .src_line {
+                white-space: pre-wrap;
+            }
         }
     }
 

default_environment/templates/html/src_block.dust

@@ -5,7 +5,7 @@
     <tbody>
       {#.lines}
         <tr>
-          <td><code>{.}</code></td>
+          <td><code class="src_line">{.}</code></td>
         </tr>
       {/.lines}
     </tbody>