tests: added SAUL test application

tests/saul/Makefile

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+APPLICATION = saul
+include ../Makefile.tests_common
+
+# include and auto-initialize all available sensors
+USEMODULE += saul_reg
+USEMODULE += saul_default
+USEMODULE += auto_init_saul
+
+USEMODULE += xtimer
+
+include $(RIOTBASE)/Makefile.include

tests/saul/README.md

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+Expected result
+===============
+This test application is polling all available SAUL devices periodically for
+their data. This data is then printed to STDIO.
+
+Background
+==========
+The actual devices that are actually polled depend on the devices that are
+configured for a particular platform. If you want to test the SAUL interface
+to a particular device, you should just connect it to your BOARD and include
+the corresponding device driver using the `USEMODULE` environment variable.

tests/saul/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 the SAUL interface of devices by periodically reading from
+ *              them
+ *
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ *
+ */
+
+#include <stdio.h>
+
+#include "xtimer.h"
+#include "phydat.h"
+#include "saul_reg.h"
+
+/**
+ * @brief   Read th sensors every second
+ */
+#define INTERVAL            (1000000U)
+
+
+int main(void)
+{
+    phydat_t res;
+    uint32_t last = xtimer_now();
+
+    puts("SAUL test application");
+
+    while (1) {
+        saul_reg_t *dev = saul_reg;
+
+        if (dev == NULL) {
+            puts("No SAUL devices present");
+            return 1;
+        }
+
+        while (dev) {
+            int dim = saul_reg_read(dev, &res);
+            phydat_dump(&res, dim);
+            dev = dev->next;
+        }
+
+        xtimer_usleep_until(&last, INTERVAL);
+    }
+
+    return 0;
+}