Work towards #56: Add permalink to every pattern

This makes cleaner URLs thanks to jekyll

thread-pool/index.md

@@ -2,6 +2,7 @@
 layout: pattern
 title: Thread Pool
 folder: thread-pool
+permalink: /patterns/thread-pool/
 categories: pattern_cat
 tags: pattern_tag
 ---
@@ -16,4 +17,4 @@ and eliminating the latency of creating new threads.
 
 **Applicability:** Use the Thread Pool pattern when
 
-* you have a large number of short-lived tasks to be executed in parallel
+* you have a large number of short-lived tasks to be executed in parallel