add function begin without any parameters and add functin psk to return current pre shared kex form sdk config

Author: pgollor

hardware/esp8266com/esp8266/libraries/ESP8266WiFi/keywords.txt

@@ -41,6 +41,7 @@ localIP	KEYWORD2
 subnetMask	KEYWORD2
 gatewayIP	KEYWORD2
 SSID	KEYWORD2
+psk	KEYWORD2
 BSSID		KEYWORD2
 RSSI	KEYWORD2
 encryptionType	KEYWORD2

hardware/esp8266com/esp8266/libraries/ESP8266WiFi/src/ESP8266WiFi.cpp

@@ -145,6 +145,17 @@ int ESP8266WiFiClass::begin(const char* ssid, const char *passphrase, int32_t ch
     return status();
 }
 
+int ESP8266WiFiClass::begin()
+{
+    ETS_UART_INTR_DISABLE();
+    wifi_station_connect();
+    ETS_UART_INTR_ENABLE();
+
+    if(!_useStaticIp)
+        wifi_station_dhcpc_start();
+    return status();
+}
+
 uint8_t ESP8266WiFiClass::waitForConnectResult(){
   if ((wifi_get_opmode() & 1) == 0)//1 and 3 have STA enabled
       return WL_DISCONNECTED;
@@ -366,6 +377,13 @@ char* ESP8266WiFiClass::SSID()
     return reinterpret_cast<char*>(conf.ssid);
 }
 
+const char* ESP8266WiFiClass::psk()
+{
+    static struct station_config conf;
+    wifi_station_get_config(&conf);
+    return reinterpret_cast<const char*>(conf.password);
+}
+
 uint8_t* ESP8266WiFiClass::BSSID(void)
 {
     static struct station_config conf;

hardware/esp8266com/esp8266/libraries/ESP8266WiFi/src/ESP8266WiFi.h

@@ -58,6 +58,9 @@ class ESP8266WiFiClass
     int begin(const char* ssid, const char *passphrase = NULL, int32_t channel = 0, uint8_t bssid[6] = NULL);
     int begin(char* ssid, char *passphrase = NULL, int32_t channel = 0, uint8_t bssid[6] = NULL);
 
+    // Use sdk config to connect.
+    int begin();
+
 
    /* Wait for Wifi connection to reach a result
     * returns the status reached or disconnect if STA is off
@@ -172,6 +175,13 @@ class ESP8266WiFiClass
      */
     char* SSID();
 
+    /*
+     * Return the current pre shared key associated with the network
+     *
+     * return: psk string
+     */
+    const char* psk();
+
     /*
      * Return the current bssid / mac associated with the network if configured
      *