performance improvement about ark HOT 2 CLOSED

Re-opened because I am still working on it, we can do better

from ark.

Maybe we can use a stack of Scope (vector<Value> + small overhead to know if it's owned by the VM or by a Value + maybe a ref counter if it's owned by a Value) to store the Scopes. The small overhead to know who owns the scope would be useful to know if we can delete the scope or not (garbage collection). The scopes would be pushed onto a vector<Scope*> when used. Closures would only have to hold a Scope*.

It would improve #13 and #15 as well.

Edit: tried, but it killed the performances on the ackermann peter function test, reverting

from ark.