Fix example 5.2.

Added the endpoint property and appropriate accessors to the BufferedAdd plugin and added a call to the get accessor to be passed in to the update() call.

Conflicts:
	tests/Solarium/Tests/Plugin/BufferedAdd/BufferedAddTest.php

Event AddDocument for BufferedAdd plugin

Implemented an event which is fired on each document added to the BufferAdd plugin so you can provide some more status feedback while importing.