Make Arduino timer stuff work on Contiki

New discovery: Contiki also uses timer 0. With almost the same interface
as Arduino. So we now completely get rid of wiring.c (only the main
file, the other wiring_xxx stay) and implement Arduino timer, delay, etc
in terms of the corresponding Contiki routines. Verified that now delay
works as expected. The LED in examples/osd/arduino-sketch blinks!

Before this, the arduino_init routine in wiring.c destroyed the timer-0
initialization of contiki, making both, contiki timer implementation
*and* contiki timer implementation fail if the arduino_init routine was
called. Now both work.

Squashed with following bug-fix commit.

platform/osd-merkur/dev/hw-arduino.h

@@ -48,6 +48,12 @@
  *
  */
 
+#ifdef __cplusplus
+extern "C"{
+#endif
+
+#include "contiki.h"
+
 /*
  * The OSD hardware only supports timer 3 for PWM, timer 2 is used by
  * contiki for sleep/wakeup timing and is not usable for PWM.
@@ -65,9 +71,39 @@
 #define arduino_pwm_timer_init() \
   (hwtimer_ini (3, HWT_WGM_PWM_PHASE_8_BIT, HWT_CLOCK_PRESCALER_64, 0))
 
+/*
+ * micros on arduino takes timer overflows into account.
+ * We put in the seconds counter. To get a consistent seconds / ticks
+ * value we have to disable interrupts.
+ */
+static inline uint32_t micros (void)
+{
+  uint32_t ticks;
+  uint8_t sreg = SREG;
+  cli ();
+  ticks = clock_seconds () * 1000000L
+        + clock_time () * 1000L / CLOCK_SECOND;
+  SREG = sreg;
+  return ticks;
+}
+/*
+ * millis counts only internal timer ticks since start, not trying to do
+ * something about overflows. Note that we don't try to emulate overflow
+ * behaviour of arduino implementation.
+ */
+#define millis()              (((uint32_t)clock_time())*1000L/CLOCK_SECOND)
+#define micros()              (clock_seconds()*1000L+
+#define delay(ms)             clock_delay_msec(ms)
+#define delayMicroseconds(us) clock_delay_usec(us)
+
+
 /*
  * VI settings, see coding style
  * ex:ts=8:et:sw=2
  */
 
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
 /** @} */