Work towards #56: Splitting up the README

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

iterator/index.md

@@ -0,0 +1,22 @@
+---
+layout: pattern
+title: Iterator
+folder: iterator
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** Provide a way to access the elements of an aggregate object
+sequentially without exposing its underlying representation.
+
+![alt text](./etc/iterator_1.png "Iterator")
+
+**Applicability:** Use the Iterator pattern
+
+* to access an aggregate object's contents without exposing its internal representation
+* to support multiple traversals of aggregate objects
+* to provide a uniform interface for traversing different aggregate structures
+
+**Real world examples:**
+
+* [java.util.Iterator](http://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html)