Show markdown description text on item detail page

* Update build process to *not* copy over prerendered pages during a
  regular build (only during a `dist` build)
* Add dependency on npm "markdown" package and include it in the
  scripts loaded in the default layout
* Update the Item model to be able to load from a *.cg file
* Add an ItemParser to process the `item.cg` file
* Update the general parser to be able to work with HereDoc-style
  text blocks
* Add a markdown-specific stylesheet
* Add a sample of the `item.cg` file format (Advanced Crafting Table)

src/jade/layouts/basic.jade

@@ -34,4 +34,5 @@ html
                 script(src="/js/jquery.js")
                 script(src="/js/backbone.js")
                 script(src="/js/jade.js")
+                script(src="/js/markdown.js")
                 script(src="/js/when.js")

src/jade/templates/item_page.jade

@@ -15,7 +15,10 @@
     .mainBody
         h1.name
         .byline: p from <a></a>
-        .description: p
+
+        .description.section
+            h2 Description
+            .panel.markdown
 
         .recipes.section
             h2 Recipes