examples: added Arduino hello-world example

examples/arduino_hello-world/Makefile

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+# name of your application
+APPLICATION = arduino_hello-world
+
+# 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)/../..
+
+USEMODULE += arduino
+
+# 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/arduino_hello-world/README.md

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+examples/arduino_hello-world
+============================
+This application demonstrates the usage of Arduino sketches in RIOT.
+
+The sketch itself is fairly simple. On startup, it initializes the LED pin to
+output mode, starts the serial port with a baudrate of 115200 and prints
+"Hello Arduino!" on the serial port. When running, the application echoes any
+newline terminated string that was received on the serial port, while toggling
+the default LED with a 1Hz frequency.
+
+The sketch just uses some very primitive Arduino API elements for demonstration
+purposes:
+- control of digital pins (pinMode(), digital read and write)
+- the delay() function
+- reading and writing the serial port using the Serial class
+
+Arduino and RIOT
+================
+For information on the Arduino support in RIOT please refer to the API
+documentation at http://doc.riot-os.org/group__sys__arduino.html
+
+Usage
+=====
+Just send any newline terminated string to the board's serial port, and the
+board will echo this string.
+
+Example output
+==============
+When using pyterm, the output will look similar to this:
+```
+2015-11-26 14:04:58,307 - INFO # main(): This is RIOT! (Version: xxx)
+2015-11-26 14:04:58,308 - INFO # Hello Arduino!
+hello again
+2015-11-26 14:06:29,800 - INFO # Echo: hello again
+are you still there?
+2015-11-26 14:06:48,301 - INFO # Echo: are you still there?
+
+```
+If your board is equipped with an on-board LED, you should see this LED toggling
+every half a second.
+
+NOTE: if your board's STDIO baudrate is not configured to be 115200 (see your
+board's `board.h`), the first line of the output may not be shown or scrambled.

examples/arduino_hello-world/hello-world.sketch

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+/*
+  Arduino Hello-World @ RIOT
+  Prints 'Hello Arduino!' once on the serial port during startup, toggles the
+  default LED twice each seconds and echoes incoming characters on the serial
+  port.
+ */
+
+// Per convention, RIOT defines a macro that is assigned the pin number of an
+// on-board LED. If no LED is available, the pin number defaults to 0. For
+// compatibility with the Arduino IDE, we also fall back to pin 0 here, if the
+// RIOT macro is not available
+#ifndef ARDUINO_LED
+#define ARDUINO_LED     (0)
+#endif
+
+// Assign the default LED pin
+int ledPin = ARDUINO_LED;
+
+// input buffer for receiving chars on the serial port
+int buf[64];
+
+// counter that counts the number of received chars
+int count = 0;
+
+void setup(void)
+{
+    // configure the LED pin to be output
+    pinMode(ledPin, OUTPUT);
+    // configure the first serial port to run with a baudrate of 115200
+    Serial.begin(115200);
+    // say hello
+    Serial.println("Hello Arduino!");
+}
+
+void loop(void)
+{
+    // toggle the LED
+    digitalWrite(ledPin, !digitalRead(ledPin));
+    // test if some chars were received
+    while (Serial.available() > 0) {
+        // read a single character
+        int tmp = Serial.read();
+        // if we got a line end, we echo the buffer
+        if (tmp == '\n') {
+            // start with printing 'ECHO: '
+            Serial.write("Echo: ");
+            // echo the buffer
+            for (int i = 0; i < count; i++) {
+                Serial.write(buf[i]);
+            }
+            // terminate the string with a newline
+            Serial.write('\n');
+            // reset the count variable
+            count = 0;
+        }
+        // else we just remember the incoming char
+        else {
+            buf[count++] = tmp;
+        }
+    }
+    // wait for half a second
+    delay(500);
+}