First refactor of Report

Because you challenged me to tackle report.rb.. here goes :
 - The initialisers have been moved to their own files
 - The renderer is now a separate object, making refactoring easier and the namespace less polluted
 - Thanks to the renderer refactor it is now possible to refactor common methods. I've refactored array rendering into a single function, cleaning up the code a lot. This saves about 25% lines of code.

This new structure opens up possibilities to do more refactoring.