Memory checks for arrays

# Example code
```python
routine main() is
	var x : array[5] integer;
	x[-1] := -1;
	x[0] := 0;
	x[6] := 6;
	println x[-1];
	println x[0];
	println x[6];
	return;
end
```

## Expected behavor
Runtime errors as we access invalid indexes (btw, C+ arrays are 1-indexed)

## Actual behavior
Prints -1, 0, 6
Although seems cool, it shouldn't be like this.
