Minor improvements to classom.badlogic.gdx.utils. Array<T>

Changes to class com.badlogic.gdx.utils. Array<T>

1) ArrayIterator attribute now has the generic type T.
2) add, addAlland removeAll methods now accepts Array objects of type T or types derived from type T.
3) Generic type added in the creation of the iterator in the iterator() method.
4) Class ArrayIterable seems to have no utility. It has been deleted.
5) Documentation has been added to methods add and addAll.

Regards.


Signed-off-by: Javier J. <javierj@us.es>