Implement multiple-dimension array access notification

[codingpotato]

Fix #189

Run following code in SeedLang.Shell to see the notifications.

a = [1, 2, 3]
print(a)  # [1, 2, 3]

a[1] = [1, 2, 3]
print(a)  # [1, [1, 2, 3], 3]

a[1][1] = [1, 2, 3]
print(a)  # [1, [1, [1, 2, 3], 3], 3]

a[1][1][1] = 5
print(a)  # [1, [1, [1, 5, 3], 3], 3]