Work towards #56: Splitting up the README

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

adapter/index.md

@@ -0,0 +1,23 @@
+---
+layout: pattern
+title: Adapter
+folder: adapter
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** Convert the interface of a class into another interface the clients
+expect. Adapter lets classes work together that couldn't otherwise because of
+incompatible interfaces.
+
+![alt text](./etc/adapter_1.png "Adapter")
+
+**Applicability:** Use the Adapter pattern when
+
+* you want to use an existing class, and its interface does not match the one you need
+* you want to create a reusable class that cooperates with unrelated or unforeseen classes, that is, classes that don't necessarily have compatible interfaces
+* you need to use several existing subclasses, but it's impractical to adapt their interface by subclassing every one. An object adapter can adapt the interface of its parent class.
+
+**Real world examples:**
+
+* [java.util.Arrays#asList()](http://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#asList%28T...%29)