3rd ed., Item46, Refine run_cascading() function

The function `run_cascading()` of Item 46 can be improved as follows: 


```python
def run_cascading():
    amplitudes = [7, 7, 7, 2, 2, 2, 2, 10, 10, 10, 10, 10]
    it = complex_wave_cascading(iter(amplitudes))  # Iterator
    for output in it:
        transmit(output)
```
