Add LIN_ADVANCE

Marlin/Configuration_adv.h

@@ -457,6 +457,15 @@
   #define MESH_MAX_Y (Y_MAX_POS - (MESH_INSET))
 #endif
 
+//Implementation of a linear pressure control
+//Assumption: advance = k * (delta velocity)
+//K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+#define LIN_ADVANCE
+
+#if ENABLED(LIN_ADVANCE)
+  #define LIN_K 75
+#endif
+
 // @section extras
 
 // Arc interpretation settings: