Improve code generators consistency

[neeckeloo]

I added formArray() method in some generators for consistency.

[neeckeloo]

I think it would be judicious to create a static method \Zend\Code\Generator\AbstractGenerator::fromArray() a bit like \Zend\Stdlib\AbstractOptions::setFromArray() to reduce code and for consistency of all generators. There still remains the possibility of extending this method if necessary.

@weierophinney Do you think I can refactor the code from this idea ?

[weierophinney]

@neeckeloo The only issue with abstracting it is that not all of them have the same properties/methods that they operate on -- it looked like each one had a slight variation of one sort or another. As such, I think having each define their specific functionality is good here.