data provider rewrite a bit the documentation

[Grummfy]

For now data provider are there :
http://docs.atoum.org/en/latest/annotations.html#data-provider

Just make one explicit example, then sub catagory with the differents ways like now :

• data provider as protected method
• data provider as closure
• data provider as injected ...
• data provider as annotation

Create a new chapter for the data provider, isntead of letting it inside annotation.

The purpose is to make it more explicit and understable