Bug:List to tuple conversion

Dear developers,

It seems to me that Codon is unable to perform a simple conversion from a list to a tuple. Here is a minimal example:

```python
l = [1, 2]
t = tuple[int, int](l)
print(t)
```

The Python output is obviously `(1, 2)`, but Codon 0.16.3 complains with this error:

```
b.py:2:5-23: error: 'Tuple[int,int]' object has no method '__new__' with arguments (List[int])
```

This is a major nuissance as, many times, lists must be converted to tuples to insert them into dicts.