examples: added stand-alone SAUL example

examples/saul/Makefile

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+# name of your application
+APPLICATION = default
+
+# If no BOARD is found in the environment, use this default:
+BOARD ?= native
+
+# This has to be the absolute path to the RIOT base directory:
+RIOTBASE ?= $(CURDIR)/../..
+
+# we want to use SAUL:
+USEMODULE += saul_default
+# include the shell:
+USEMODULE += shell
+USEMODULE += shell_commands
+# additional modules for debugging:
+USEMODULE += ps
+
+# Comment this out to disable code in RIOT that does safety checking
+# which is not needed in a production environment but helps in the
+# development process:
+CFLAGS += -DDEVELHELP
+
+# Change this to 0 show compiler invocation lines by default:
+QUIET ?= 1
+
+include $(RIOTBASE)/Makefile.include

examples/saul/README.md

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+examples/saul
+================
+This application demonstrates the usage of SAUL and the SAUL registry.
+
+Usage
+=====
+Simply build and flash the application for your target board:
+```
+BOARD=YOUR_BOARD_NAME_HERE make flash term
+```
+
+Now you should have access to the RIOT shell on your board. For interacting
+with SAUL devices, use the `saul` shell command, e.g.:
+```
+saul            <- this will list all available devices mapped into
+                   the SAUL registry
+saul read 0     <- read values from device #0
+saul write 1 0  <- write a `0` to SAUL device #1
+```

examples/saul/main.c

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+/*
+ * Copyright (C) 2017 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     examples
+ * @{
+ *
+ * @file
+ * @brief       Example for demonstrating SAUL and the SAUL registry
+ *
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "shell.h"
+
+int main(void)
+{
+    puts("Welcome to RIOT!\n");
+    puts("Type `help` for help, type `saul` to see all SAUL devices\n");
+
+    char line_buf[SHELL_DEFAULT_BUFSIZE];
+    shell_run(NULL, line_buf, SHELL_DEFAULT_BUFSIZE);
+
+    return 0;
+}