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/scss/templates/item_page.scss

@@ -31,15 +31,6 @@ All rights reserved.
             }
         }
 
-        .description {
-            margin-bottom: 4em;
-
-            p {
-                font-family: $font-family-normal;
-                font-size: $font-size-large;
-            }
-        }
-
         .recipes {
             display: none;