Initial implementation of avr hardware timer

Mainly for PWM use for now.
With example to set the LED to different brightness via COAP.
We switch the LED with 50 kHz (20µs) in this example.

examples/osd/pwm-example/led_pwm.h

@@ -0,0 +1,26 @@
+/**
+ * \defgroup LED PWM example
+ *
+ * Resource definition for LED PWM module
+ *
+ * @{
+ */
+
+/**
+ * \file
+ *         Resource definitions for the LED PWM module
+ *      
+ * \author
+ *         Ralf Schlatterbeck <rsc@tux.runtux.com>
+ */
+
+#ifndef led_pwm_h
+#define led_pwm_h
+#include "contiki.h"
+#include "erbium.h"
+
+extern resource_t resource_led_pwm;
+extern void led_pwm_init (void);
+
+#endif // led_pwm_h
+/** @} */