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/python/ds2413.py

@@ -0,0 +1,57 @@
+#!/usr/bin/python
+# Author: Jon Trulson <jtrulson@ics.com>
+# Copyright (c) 2015 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.
+
+import time, sys, signal, atexit
+import pyupm_ds2413 as sensorObj
+
+# Instantiate a DS2413 Module on a Dallas 1-wire bus connected to UART 0
+sensor = sensorObj.DS2413(0)
+
+## Exit handlers ##
+# This stops python from printing a stacktrace when you hit control-C
+def SIGINTHandler(signum, frame):
+	raise SystemExit
+
+# This function lets you run code on exit
+def exitHandler():
+	print "Exiting..."
+	sys.exit(0)
+
+# Register exit handlers
+atexit.register(exitHandler)
+signal.signal(signal.SIGINT, SIGINTHandler)
+
+# find all of the DS2413 devices present on the bus
+sensor.init();
+
+# how many devices were found?
+print "Found", sensor.devicesFound(), "device(s)"
+
+# 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>
+print "GPIO device 0 values:", sensor.readGpios(0)
+
+# set the gpio latch values of the first device
+print "Setting GPIO latches to on"
+sensor.writeGpios(0, 0x03);