Merge: Nitin tests

Add a basic test for the nit interactive interpreter.

I also added a new engine but most test fails because:

Local variables in main are too much local, so the following fail because `a` is unknown in the second line. I plan to solve this problem.

~~~
var a = 1
print a
~~~

Classes and top-level methods are analysed one after the other so the following fails because `B` is unknown while processing the first class. I do not plan to solve this problem as I think this is the expected behavior when interactive.

~~~
class A
   var b: B
end
class B
end
~~~

Pull-Request: #2410