Work towards #56: Add permalink to every pattern

This makes cleaner URLs thanks to jekyll

private-class-data/index.md

@@ -2,6 +2,7 @@
 layout: pattern
 title: Private Class Data
 folder: private-class-data
+permalink: /patterns/private-class-data/
 categories: pattern_cat
 tags: pattern_tag
 ---
@@ -14,4 +15,4 @@ attributes by encapsulating them in single Data object.
 
 **Applicability:** Use the Private Class Data pattern when
 
-* you want to prevent write access to class data members
+* you want to prevent write access to class data members