Fix compiler issues due to SofwareSerial

When SerialFirmata was extracted from StandardFirmataPlus to a
separate class it broke the ability to compile Firmata with
versions of the Arduino IDE older than 1.6.6. This is because
prior to 1.6.6 Arduino did not allow libraries to include other
libraries unless the other library was included in the sketch.
In this particular case that was not possible because
SerialFirmata is compiled before the sketch is compiled.

There were a couple of potential work arounds:
1. Only include SoftwareSerial when compiling in Arduino 1.6.6 or
   higher.
2. Split SerialFirmata into SoftwareSerialFirmata and
   HardwareSerialFirmata and then include SoftwareSerial in the
   sketch if SoftwareSerialFirmata is included. However this
   requires the user to modify the sketch.

I opted for option 1. If users really need to use software serial
with SerialFirmata in Arduino 1.6.5 or older, I can reconsider
option 2 at a later time.

Author: soundanalogous

examples/StandardFirmataBLE/StandardFirmataBLE.ino

@@ -34,6 +34,8 @@
  * Uncomment the following include to enable interfacing
  * with Serial devices via hardware or software serial.
  */
+// In order to use software serial, you will need to compile this sketch with
+// Arduino IDE v1.6.6 or higher. Hardware serial should work back to Arduino 1.0.
 //#include "utility/SerialFirmata.h"
 
 // follow the instructions in bleConfig.h to configure your BLE hardware

examples/StandardFirmataEthernet/StandardFirmataEthernet.ino

@@ -78,6 +78,8 @@
  * remaining to reliably run Firmata. Arduino Yun is okay because it doesn't import the Ethernet
  * libraries.
  */
+// In order to use software serial, you will need to compile this sketch with
+// Arduino IDE v1.6.6 or higher. Hardware serial should work back to Arduino 1.0.
 //#include "utility/SerialFirmata.h"
 
 #define I2C_WRITE                   B00000000

examples/StandardFirmataPlus/StandardFirmataPlus.ino

@@ -20,7 +20,7 @@
 
   See file LICENSE.txt for further informations on licensing terms.
 
-  Last updated by Jeff Hoefs: January 10th, 2016
+  Last updated October 16th, 2016
 */
 
 /*
@@ -36,6 +36,9 @@
   - Ability to interface with serial devices using UART, USART, or SoftwareSerial
     depending on the capatilities of the board.
 
+  NOTE: In order to use SoftwareSerial with the Firmata Serial feature,
+  StandardFirmataPlus must be compiled with Arduino v1.6.6 or newer.
+
   At the time of this writing, StandardFirmataPlus will still compile and run
   on ATMega328p and ATMega32u4-based boards, but future versions of this sketch
   may not as new features are added.
@@ -45,6 +48,8 @@
 #include <Wire.h>
 #include <Firmata.h>
 
+// In order to use software serial, you will need to compile this sketch with
+// Arduino IDE v1.6.6 or higher. Hardware serial should work back to Arduino 1.0.
 #include "utility/SerialFirmata.h"
 
 #define I2C_WRITE                   B00000000

examples/StandardFirmataWiFi/StandardFirmataWiFi.ino

@@ -89,6 +89,8 @@
  * Uncomment the following include to enable interfacing with Serial devices via hardware or
  * software serial.
  */
+// In order to use software serial, you will need to compile this sketch with
+// Arduino IDE v1.6.6 or higher. Hardware serial should work back to Arduino 1.0.
 //#include "utility/SerialFirmata.h"
 
 // follow the instructions in wifiConfig.h to configure your particular hardware

utility/SerialFirmata.cpp

@@ -14,17 +14,19 @@
 
   - handlePinMode calls Firmata::setPinMode
 
-  Last updated by Jeff Hoefs: January 10th, 2016
+  Last updated October 16th, 2016
 */
 
 #include "SerialFirmata.h"
 
 SerialFirmata::SerialFirmata()
 {
+#if defined(SoftwareSerial_h)
   swSerial0 = NULL;
   swSerial1 = NULL;
   swSerial2 = NULL;
   swSerial3 = NULL;
+#endif
 
   serialIndex = -1;
 }

utility/SerialFirmata.h

@@ -15,18 +15,18 @@
   - Defines FIRMATA_SERIAL_FEATURE (could add to Configurable version as well)
   - Imports Firmata.h rather than ConfigurableFirmata.h
 
-  Last updated by Jeff Hoefs: January 10th, 2016
+  Last updated October 16th, 2016
 */
 
 #ifndef SerialFirmata_h
 #define SerialFirmata_h
 
 #include <Firmata.h>
 #include "FirmataFeature.h"
-// SoftwareSerial is currently only supported for AVR-based boards and the Arduino 101
-// The third condition checks if the IDE is in the 1.0.x series, if so, include SoftwareSerial
-// since it should be available to all boards in that IDE.
-#if defined(ARDUINO_ARCH_AVR) || defined(ARDUINO_ARCH_ARC32) || (ARDUINO >= 100 && ARDUINO < 10500)
+// SoftwareSerial is currently only supported for AVR-based boards and the Arduino 101.
+// Limited to Arduino 1.6.6 or higher because Arduino builder cannot find SoftwareSerial
+// prior to this release.
+#if (ARDUINO > 10605) && (defined(ARDUINO_ARCH_AVR) || defined(ARDUINO_ARCH_ARC32))
 #include <SoftwareSerial.h>
 #endif
 
@@ -155,10 +155,12 @@ class SerialFirmata: public FirmataFeature
     int serialBytesToRead[SERIAL_READ_ARR_LEN];
     signed char serialIndex;
 
+#if defined(SoftwareSerial_h)
     Stream *swSerial0;
     Stream *swSerial1;
     Stream *swSerial2;
     Stream *swSerial3;
+#endif
 
     Stream* getPortFromId(byte portId);