Work towards #56: Splitting up the README

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

bridge/index.md

@@ -0,0 +1,21 @@
+---
+layout: pattern
+title: Bridge
+folder: bridge
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** Decouple an abstraction from its implementation so that the two can
+vary independently.
+
+
+![alt text](./etc/bridge_1.png "Bridge")
+
+**Applicability:** Use the Bridge pattern when
+
+* you want to avoid a permanent binding between an abstraction and its implementation. This might be the case, for example, when the implementation must be selected or switched at run-time.
+* both the abstractions and their implementations should be extensible by subclassing. In this case, the Bridge pattern lets you combine the different abstractions and implementations and extend them independently
+* changes in the implementation of an abstraction should have no impact on clients; that is, their code should not have to be recompiled.
+* you have a proliferation of classes. Such a class hierarchy indicates the need for splitting an object into two parts. Rumbaugh uses the term "nested generalizations" to refer to such class hierarchies
+* you want to share an implementation among multiple objects (perhaps using reference counting), and this fact should be hidden from the client. A simple example is Coplien's String class, in which multiple objects can share the same string representation.