add styling to code blocks (thanks @epwalsh)

Author: daattali

css/main.css

@@ -596,4 +596,8 @@ pre {
   background-repeat: repeat;
   background-size: 3em 3em;
   border-left: 7px solid #444;
-}
+}
+
+pre code {
+  white-space: pre;
+}