Queued fan control. Issue #90

Marlin/planner.h

@@ -59,6 +59,7 @@ typedef struct {
   unsigned long initial_rate;                        // The jerk-adjusted step rate at start of block  
   unsigned long final_rate;                          // The minimal rate at exit
   unsigned long acceleration_st;                     // acceleration steps/sec^2
+  unsigned long fan_speed;
   volatile char busy;
 } block_t;