Add the socalled "Babystepping" feature.

It is a realtime control over the head position via the LCD menu system that works _while_ printing.
Using it, one can e.g. tune the z-position in realtime, while printing the first layer.
Also, lost steps can be manually added/removed, but thats not the prime feature.
Stuff is placed into the Tune->Babystep *

It is not possible to have realtime control via gcode sending due to the buffering, so I did not include a gcode yet. However, it could be added, but it movements will not be realtime then.

Historically, a very similar thing was implemented for the "Kaamermaker" project, while Joris was babysitting his offspring, hence the name.

say goodby to fuddling around with the z-axis.

Marlin/stepper.h

@@ -92,4 +92,10 @@ void digipot_current(uint8_t driver, int current);
 void microstep_init();
 void microstep_readings();
 
+#ifdef BABYSTEPPING
+  void babystep(const uint8_t axis,const bool direction); // perform a short step with a single stepper motor, outside of any convention
+#endif
+     
+
+
 #endif