add support for list of AP connections

- auto select ssid with best signal
 - for debugging enable DEBUG_WIFI_MULTI macro and call Serial.setDebugOutput(true);

change ESP8266WiFiClass::status() return type to wl_status_t

libraries/ESP8266WiFi/src/ESP8266WiFi.cpp

@@ -336,7 +336,7 @@ uint8_t ESP8266WiFiClass::encryptionType(uint8_t i)
     return -1;
 }
 
-uint8_t ESP8266WiFiClass::status()
+wl_status_t ESP8266WiFiClass::status()
 {
     int status = wifi_station_get_connect_status();