[Enhancement] add List.resize(n)

[khchen]

Add resize method to List class. Example:

l = [1, 2, 3, 4, 5]
print(l)

l.resize(3)
print(l)

l.resize(5)
print(l)

Output:

[1, 2, 3, 4, 5]
[1, 2, 3]
[1, 2, 3, null, null]