ds2413: Initial implementation

This adds initial support for the DS2413 Dual Channel Addressable
Switch.  This is a Dallas Semiconductor 1-wire compliant device
providing access to 2 open-drain GPIOs.

https://learn.adafruit.com/adafruit-1-wire-gpio-breakout-ds2413/overview

This driver requires One-Wire over UART support in MRAA (PR #415)
which is not yet merged.

Signed-off-by: Jon Trulson <jtrulson@ics.com>

examples/c++/ds2413.cxx

@@ -0,0 +1,59 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2016 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <unistd.h>
+#include <iostream>
+#include <stdio.h>
+#include "ds2413.h"
+
+using namespace std;
+using namespace upm;
+
+int main(int argc, char **argv)
+{
+//! [Interesting]
+  // Instantiate a DS2413 Module on a Dallas 1-wire bus connected to UART 0
+  upm::DS2413* sensor = new upm::DS2413(0);
+
+  // find all of the DS2413 devices present on the bus
+  sensor->init();
+
+  // how many devices were found?
+  cout << "Found "<< sensor->devicesFound() << " device(s)" << endl;
+
+  // read the gpio and latch values from the first device
+  // the lower 4 bits are of the form:
+  // <gpioB latch> <gpioB value> <gpioA latch> <gpioA value>
+  cout << "GPIO device 0 values: " << sensor->readGpios(0) << endl;
+
+  // set the gpio latch values of the first device
+  cout << "Setting GPIO latches to on" << endl;
+  sensor->writeGpios(0, 0x03);
+
+  cout << "Exiting..." << endl;
+
+  delete sensor;
+//! [Interesting]
+  return 0;
+}