tests: added test app for the bh1750fvi driver

tests/driver_bh1750/Makefile

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+APPLICATION = driver_pir
+include ../Makefile.tests_common
+
+USEMODULE += xtimer
+USEMODULE += bh1750fvi
+
+include $(RIOTBASE)/Makefile.include

tests/driver_bh1750/README.md

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+# About
+This test application is created for testing/demonstrating the BH1750FVI driver.
+It uses the default device parameters as specified in
+`drivers/bh1750fvi/include/bh1750fvi_params.h`. To override these setting, you
+can simply do this by defining these parameters as compiler flags while uilding,
+e.g.:
+```
+$ CFLAGS="-DBH1750FVI_PARAM_I2C=I2C_DEV(1)"" make all
+```
+
+# Usage
+Simply flash this example to your board and it will read the sensor value 5
+times per second and print the sampled value to STDIO. You can verify the values
+by simply covering the sensor or holding it in front of a bright light and see
+the change in the sensor readings accordingly.

tests/driver_bh1750/main.c

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+/*
+ * Copyright (C) 2016 Freie Universität Berlin
+ *
+ * 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 BH1750FVI ambient light sensor driver
+ *
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "xtimer.h"
+#include "bh1750fvi.h"
+#include "bh1750fvi_params.h"
+
+#define RATE        (200 * MS_IN_USEC)      /* 200ms */
+
+int main(void)
+{
+    bh1750fvi_t dev;
+    uint32_t last = xtimer_now();
+
+    puts("BH1750FVI ambient light sensor test\n");
+
+    /* initialize the device */
+    bh1750fvi_init(&dev, (bh1750fvi_params_t *)(&bh1750fvi_params));
+
+    /* periodically sample the sensor */
+    while(1) {
+        uint16_t val = bh1750fvi_sample(&dev);
+        printf("value: %5i lux\n", (int)val);
+        xtimer_usleep_until(&last, RATE);
+    }
+
+    return 0;
+}