ds18b20: Add a C implementation and inprove documentation

This commit adds a C implementation for the DS18B20.  The C++
implementation was untouched (ie: it does not wrap the C
implementation).  This can be done in the future if desired.

In addition, add an ascii-schematic to both the .h and .hpp files to
better illustrate how to wire up the DS 1-wire interface for the UART.

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

examples/c/CMakeLists.txt

@@ -116,6 +116,7 @@ add_example (tsl2561)
 add_example (collision)
 add_example (moisture)
 add_example (led)
+add_example (ds18b20)
 
 # Custom examples
 add_custom_example (nmea_gps_i2c-example-c nmea_gps_i2c.c nmea_gps)

examples/c/ds18b20.c

@@ -0,0 +1,81 @@
+/*
+ * 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 <stdio.h>
+#include <signal.h>
+
+#include "ds18b20.h"
+
+bool shouldRun = true;
+
+void sig_handler(int signo)
+{
+  if (signo == SIGINT)
+    shouldRun = false;
+}
+
+int main(int argc, char **argv)
+{
+  signal(SIGINT, sig_handler);
+
+//! [Interesting]
+
+  printf("Initializing...\n");
+
+  // Instantiate an DS18B20 instance using the uart 0
+  ds18b20_context sensor = ds18b20_init(0);
+
+  if (!sensor)
+    {
+      printf("ds18b20_init() failed.\n");
+      return(1);
+    }
+
+  printf("Found %d device(s)\n\n", ds18b20_devices_found(sensor));
+
+  // update and print available values every second
+  while (shouldRun)
+    {
+      // update our values for all sensors
+      ds18b20_update(sensor, -1);
+
+      int i;
+      for (i=0; i<ds18b20_devices_found(sensor); i++)
+        {
+          printf("Device %02d: Temperature: %f C\n",
+                 i, ds18b20_get_temperature(sensor, i));
+        }
+      printf("\n");
+
+      sleep(2);
+    }
+
+  printf("Exiting...\n");
+
+  ds18b20_close(sensor);
+//! [Interesting]
+
+  return 0;
+}