examples: C/C++ examples use transitive dependencies

Updated the examples to comprehend transitive dependencies.  This means
that each example target will no longer have a giant list of -I includes
(the examples at the end of the list had includes for all previous
examples, upwards of 200 -I's on the command line).

    * Created a CMakeLists.txt in the upm/examples directory, moved
      common functionality to this level.
    * C/C++ examples now look to the filename for their dependency
      target name, ie; gas-mq2.cxx adds a dependency to the 'gas' target
    * Updated a handful of C/C++ example names to reflect this
    * Example CMake flow - glob the list of files, add targets for any
      special case examples, then att targets for all the rest

Signed-off-by: Noel Eck <noel.eck@intel.com>

examples/c/bmp280-bme280.c

@@ -0,0 +1,89 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2017 Intel Corporation.
+ *
+ * The MIT License
+ *
+ * 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 "upm_utilities.h"
+#include "bmp280.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]
+
+    // Instantiate a BME280 instance using default i2c bus and
+    // address.  We use the BMP280 driver to do all of our work, since
+    // the BMP280 and the BME280 are identical except for the fact
+    // that the BME280 includes a humidity sensor.
+    bmp280_context sensor = bmp280_init(BME280_DEFAULT_I2C_BUS,
+                                        BME280_DEFAULT_ADDR, -1);
+
+    if (!sensor)
+    {
+        printf("bmp280_init() failed\n");
+        return 1;
+    }
+
+    // For SPI, bus 0, you would pass -1 as the address, and a valid pin for CS:
+    // bmp280_init(BME280_DEFAULT_SPI_BUS,
+    //             -1, 10)
+
+    while (shouldRun)
+    {
+        // update our values from the sensor
+        if (bmp280_update(sensor))
+        {
+            printf("bmp280_update() failed\n");
+            bmp280_close(sensor);
+            return 1;
+        }
+
+        printf("Compensation Temperature: %f C\n",
+               bmp280_get_temperature(sensor));
+        printf("Pressure: %f Pa\n", bmp280_get_pressure(sensor));
+        printf("Computed Altitude: %f m\n", bmp280_get_altitude(sensor));
+        printf("Relative Humidity: %f %%\n\n", bmp280_get_humidity(sensor));
+
+        upm_delay(1);
+    }
+//! [Interesting]
+
+    printf("Exiting...\n");
+
+    bmp280_close(sensor);
+
+    return 0;
+}