Work towards #56: Add permalink to every pattern

This makes cleaner URLs thanks to jekyll

service-layer/index.md

@@ -2,6 +2,7 @@
 layout: pattern
 title: Service Layer
 folder: service-layer
+permalink: /patterns/service-layer/
 categories: pattern_cat
 tags: pattern_tag
 ---
@@ -18,4 +19,4 @@ its business logic. The Service Layer fulfills this role.
 **Applicability:** Use the Service Layer pattern when
 
 * you want to encapsulate domain logic under API
-* you need to implement multiple interfaces with common logic and data
+* you need to implement multiple interfaces with common logic and data