Add option to stop sending beacons

Add option -G, which will prevent our fake AP to ever send any beacon frame
Typo
Add options -p and -m for geolocation attack

Option -p allows one to reply to probe requests containing empty SSID with
custom SSID(s)
Option -m allows one to pass a list of BSSID and SSID used to fake APs.
The list's entries must have the form BSSID:SSID
Add usage about new options -G, -p and -m
When MAC is filtered with -d, send beacons only to that MAC