Work towards #56: Add permalink to every pattern

This makes cleaner URLs thanks to jekyll

null-object/index.md

@@ -2,6 +2,7 @@
 layout: pattern
 title: Null Object
 folder: null-object
+permalink: /patterns/null-object/
 categories: pattern_cat
 tags: pattern_tag
 ---
@@ -19,4 +20,4 @@ Object is very predictable and has no side effects: it does nothing.
 
 **Applicability:** Use the Null Object pattern when
 
-* you want to avoid explicit null checks and keep the algorithm elegant and easy to read.
+* you want to avoid explicit null checks and keep the algorithm elegant and easy to read.