Export scan method

[hitochan777]

I am not sure if I am doing the right thing but I am submitting this PR so that I can discuss the issue I am facing right now. I understand that scan can be used to get info of all available APs but it is not imported in __init__.py. So I import the method in the file so that I can import the method from the library.

~~I don't know why but get_iwconfig only returns the info of currently used AP, where I am supposed to get multiple results. Do you have any idea of why this is happening?~~

>>> iwlib.scan("wlan0")
[{'Mode': b'Master', 'ESSID': b'ESSID_HERE', 'Access Point': b'MAC_ADDRESS_HERE', 'BitRate': b'54 Mb/s', 'stats': {'quality': 47, 'level': 193, 'noise': 0, 'updated': 75}}]

~~I confirmed there are multiple APs (16) detected with iw. Is this somehow related to sudo privilege?~~

$ sudo iw wlan0 scan | grep "SSID:" | wc -l
16

UPDATE: After I turned off and on WiFi, I am now able to get multiple APs.