Fix documentation links

Author: colinodell

docs/2.0/extensions/default-attributes.md

@@ -2,6 +2,7 @@
 layout: default
 title: Default Attributes Extension
 description: The DefaultAttributesExtension allows you to apply default HTML classes and other attributes using configuration options.
+redirect_from: /extensions/default-attributes/
 ---
 
 # Default Attributes

docs/2.0/extensions/description-lists.md

@@ -2,6 +2,7 @@
 layout: default
 title: Description List Extension
 description: The Description List extension adds support for Markdown Extra-style <dl> lists
+redirect_from: /extensions/description-lists/
 ---
 
 # Description List Extension

docs/_data/menu.yml

@@ -18,6 +18,7 @@ version:
             'Attributes': '/2.0/extensions/attributes/'
             'Autolinks': '/2.0/extensions/autolinks/'
             'Default Attributes': '/2.0/extensions/default-attributes/'
+            'Description Lists': '/2.0/extensions/description-lists/'
             'Disallowed Raw HTML': '/2.0/extensions/disallowed-raw-html/'
             'External Links': '/2.0/extensions/external-links/'
             'Footnotes': '/2.0/extensions/footnotes/'