connection state management modified

[jnsbyr]

• check member _connected first in connect_client() to prevent querying
  connected() of disconnected _client
• added method status() to check TCP connection state (ESP8266 only)

[jnsbyr]

This change may help to resolve the cross platform connect/disconnect issues mentioned here.

For the ESP8266 an additional change is required that is not included in this merge request. At least when SERIAL_DEBUG is enabled, calling pinMode(1, OUTPUT); indirectly in systemResetCallback() causes a hang/crash at startup with 1 being the serial TX pin already in use. A possible solution could be:

  for (byte i = 0; i < TOTAL_PINS; i++) {
    // pins with analog capability default to analog input
    // otherwise, pins default to digital output
    if (IS_PIN_ANALOG(i)) {
      // turns off pullup, configures everything
      setPinModeCallback(i, PIN_MODE_ANALOG);
    } else if (IS_PIN_DIGITAL(i)) {
#if defined(ESP8266)      
      if (i == 1) continue;
#endif      
      // sets the output to 0, configures portConfigInputs
      setPinModeCallback(i, OUTPUT);
    }

With these two changes combined connect and disconnect is signalled each time in client and server mode on the ESP8266.

[soundanalogous]

This should probably use a pin ignore macro:

#define IS_IGNORE_ESP8266(p) ((p) == 1 && SERIAL_DEBUG)

I can add this later since I actually want to simplify this to use a single IS_IGNORE_PIN macro rather than being architecture specific which will remove a few more #ifdefs from StandardFirmataWiFi.

[jnsbyr]

Made another test that confirms that the issue with pin 1 only arises when SERIAL_DEBUG is enabled.

Another temporary way to avoid the pin 1 issue could be to add Firmata.setPinMode(1, PIN_MODE_IGNORE); to ignoreWiFiPins() for the ESP8266 with SERIAL_DEBUG.

The IS_IGNORE_PIN approach that you suggest is the better solution though.

[soundanalogous]

Tested in both client and server modes with all of my Wi-Fi boards and shields and everything is working as expected. Merging...