Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

specification/index.md

@@ -0,0 +1,19 @@
+---
+layout: pattern
+title: Specification
+folder: specification
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** Specification pattern separates the statement of how to match a
+candidate, from the candidate object that it is matched against. As well as its
+usefulness in selection, it is also valuable for validation and for building to
+order
+
+![alt text](./etc/specification.png "Specification")
+
+**Applicability:** Use the Specification pattern when
+
+* you need to select a subset of objects based on some criteria, and to refresh the selection at various times
+* you need to check that only suitable objects are used for a certain role (validation)