Add support for pre elements in drawer

Author: digitalcraftsman

exampleSite/content/getting-started/index.md

@@ -206,9 +206,10 @@ Once you created your first content files you can link them manually in the side
   name   = "Material"
   url    = "/"
   weight = 0
+  pre    = ""
 ```
 
-`name` is the title displayed in the menu and `url` the relative URL to the content. The `weight` attribute allows you to modify the order of the menu entries. A menu entry appears further down the more weight you add.
+`name` is the title displayed in the menu and `url` the relative URL to the content. The `weight` attribute allows you to modify the order of the menu entries. A menu entry appears further down the more weight you add. The `pre` attribute is optional and allows you to *pre*pend elements to a menu link, e.g. an icon.
 
 Instead of just linking a single file you can enhance the sidebar by creating a nested menu. This way you can list all pages of a section instead of linking them one by one (without nesting).
 

layouts/partials/nav_link.html

@@ -1,7 +1,9 @@
 {{ $currentMenuEntry := .Scratch.Get "currentMenuEntry" }}
 {{ $isCurrent := eq .Permalink ($currentMenuEntry.URL | absURL | printf "%s") }}
 
+
 <a {{ if $isCurrent }}class="current"{{ end }} title="{{ $currentMenuEntry.Name }}" href="{{ $currentMenuEntry.URL | absURL }}">
+	{{ $currentMenuEntry.Pre }}
 	{{ $currentMenuEntry.Name }}
 </a>