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/coffee/models/mod_version.coffee

@@ -171,7 +171,7 @@ module.exports = class ModVersion extends BaseModel
         return null # prevent calling `set`
 
     url: ->
-        return Url.modVersion modSlug:@modSlug, modVersion:@version
+        return Url.modVersionData modSlug:@modSlug, modVersion:@version
 
     # Object Overrides #############################################################################