tests/driver_si114x: add basic test application

tests/driver_si114x/Makefile

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+include ../Makefile.tests_common
+
+# This test should also work with Si1146 and Si1147 variants.
+USEMODULE += si1145
+
+include $(RIOTBASE)/Makefile.include

tests/driver_si114x/README.md

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+### Test application for Si114X sensors family
+
+#### Introduction
+
+The Si114X (Si1145, Si1146 and Si1147) sensors are UV, light and proximity sensors.
+More information in the [datasheet](https://www.silabs.com/Support%20Documents%2FTechnicalDocs%2FSi1145-46-47.pdf).
+
+#### Expected results
+
+After initialization, the sensor continuously (every 2 secs) displays the
+IR light, the visible light, the UV index, the proximity and the value of the
+response register.

tests/driver_si114x/main.c

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+/*
+ * Copyright (C) 2016-2018 Inria
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       Test application for the Si114x UV, IR, visible and proximity
+ *              sensor.
+ *
+ * @author      Alexandre Abadie <alexandre.abadie@inria.fr>
+ *              Bas Stottelaar <basstottelaar@gmail.com>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <inttypes.h>
+
+#include "si114x.h"
+#include "si114x_params.h"
+#include "xtimer.h"
+#include "board.h"
+
+static si114x_t dev;
+
+int main(void)
+{
+    puts("Si1145 test application\n"
+         "+------------Initializing------------+\n");
+
+    int result = si114x_init(&dev, &si114x_params[0]);
+    if (result == -SI114X_ERR_I2C) {
+        puts("[Error] The given i2c is not enabled");
+        return -1;
+    }
+    else if (result == -SI114X_ERR_NODEV) {
+        puts("[Error] The sensor did not answer correctly on the "
+             "given address");
+        return 1;
+    }
+
+    puts("Initialization successful\n"
+         "+--------Starting Measurements--------+\n");
+
+    while (1) {
+        printf("UV index: %" PRIu16 "\n"
+               "IR light [lx]: %" PRIu16 "\n"
+               "Visible light [lx]: %" PRIu16 "\n"
+               "Distance [cnt]: %" PRIu16 "\n"
+               "Response: 0x%02x\n"
+               "\n+-------------------------------------+\n",
+               si114x_read_uv(&dev),
+               si114x_read_ir(&dev),
+               si114x_read_visible(&dev),
+               si114x_read_distance(&dev),
+               si114x_read_response(&dev));
+
+        /* 2 seconds delay between measures */
+        xtimer_sleep(2);
+    }
+
+    return 0;
+}