[MicroPython feature request] WiFi scan improve.

[water5]

wifi = WLAN(mode = WLAN.STA)
wifi.scan()

MicroPython Ameba port, WiFi scan result type is 'NoneType', that not easy to access, list type is good choice. and sometimes, channel (or frequency), hidden item is useful, Ameba port have not that currently.

https://docs.micropython.org/en/latest/library/network.html#network.AbstractNIC.scan