Hid TOC on desktops & tablets, read more

* I switched the markdown engine to markdown-it.
* I used a plugin from the new engine called markdown-it-container to generate a div tag around the TOC
* Configured the plugin to generate the classname mobileOnly
* Recreated semantic's mobile only option using CSS.

public_html/styles/shared.css

@@ -58,3 +58,10 @@ footer {
 .ascend:after{
 	content: "\25BC";
 }
+
+/* device only features */
+@media screen and (min-width: 480px) {
+	.mobileOnly {
+		display: none;
+	}
+}