gsr: Added gsr sensor C source

Added the C source for the gsr sensor with necessary changes to cmake,
examples, docs.

    * Renamed all files with grovegsr to gsr
    * Replaced all instances of grovegsr with gsr
    * Added C source for gsr sensor
    * Updated all cmake files
    * Added C example for gsr sensor
    * Fixed C++ threshold method from throwing on a successfull aio read

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

examples/c/CMakeLists.txt

@@ -98,6 +98,7 @@ add_example (vdiv)
 add_example (mqx)
 add_example (o2)
 add_example (emg)
+add_example (gsr)
 
 # Custom examples
 add_custom_example (nmea_gps_i2c-example-c nmea_gps_i2c.c nmea_gps)

examples/c/gsr.c

@@ -0,0 +1,86 @@
+/*
+ * 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 <signal.h>
+
+#include "gsr.h"
+
+bool shouldRun = true;
+
+void sig_handler(int signo)
+{
+    if (signo == SIGINT)
+        shouldRun = false;
+}
+
+int main()
+{
+    signal(SIGINT, sig_handler);
+
+    //! [Interesting]
+
+    // Instantiate a gsr sensor on analog pin A0
+    gsr_context sensor = gsr_init(0);
+
+    if (!sensor)
+    {
+        printf("gsr_init() failed.\n");
+        return -1;
+    }
+
+    // Set the aref, scale, and offset
+    gsr_set_aref(sensor, 5.0);
+    gsr_set_scale(sensor, 1.0);
+    gsr_set_offset(sensor, -.1);
+    printf("aRef: %0.03f scale: %0.03f offset: %0.03f\n\n",
+            gsr_get_aref(sensor),
+            gsr_get_scale(sensor),
+            gsr_get_offset(sensor));
+
+    // Every half a second, sample the sensor output
+    while (shouldRun)
+    {
+        float normalized = 0.0;
+        float raw_volts = 0.0;
+        float volts = 0.0;
+
+        gsr_get_normalized(sensor, &normalized);
+        gsr_get_raw_volts(sensor, &raw_volts);
+        gsr_get_volts(sensor, &volts);
+
+        printf("Normalized output: %0.03f, raw gsr sensor output: %0.03f v "
+                "adjusted output: %0.03f v\n", normalized, raw_volts, volts);
+
+        usleep(500000);
+    }
+
+    //! [Interesting]
+
+    printf("Exiting\n");
+
+    gsr_close(sensor);
+
+    return 0;
+}