Work towards #56: Splitting up the README

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

abstract-factory/index.md

@@ -0,0 +1,25 @@
+---
+layout: pattern
+title: Abstract Factory
+folder: abstract-factory
+categories:
+ - pattern_cat
+ - creational
+tags: pattern_tag
+---
+
+**Intent:** Provide an interface for creating families of related or dependent
+objects without specifying their concrete classes.
+
+![alt text](./etc/abstract-factory_1.png "Abstract Factory")
+
+**Applicability:** Use the Abstract Factory pattern when
+
+* a system should be independent of how its products are created, composed and represented
+* a system should be configured with one of multiple families of products
+* a family of related product objects is designed to be used together, and you need to enforce this constraint
+* you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
+
+**Real world examples:**
+
+* [javax.xml.parsers.DocumentBuilderFactory](http://docs.oracle.com/javase/8/docs/api/javax/xml/parsers/DocumentBuilderFactory.html)