Fixed long slope at deceleration issue. Moved things into config.h. New MINIMUM_PLANNER_SPEED parameter.

- The long standing issue of a long slope at deceleration is likely
fixed. The stepper program was not tracking and timing the end of
acceleration and start of deceleration exactly and now is fixed to
start and stop on time. Also, to ensure a better acceleration curve fit
used by the planner, the stepper program delays the start of the
accelerations by a half trapezoid tick to employ the midpoint rule. -
Settings version 3 migration (not fully tested, but should work) -
Added a MINIMUM_PLANNER_SPEED user-defined parameter to planner to let
a user change this if problems arise for some reason. - Moved all
user-definable #define parameters into config.h with clear comments on
what they do and recommendations of how to change them. - Minor
housekeeping.

gcode.c

@@ -388,5 +388,4 @@ static int next_statement(char *letter, double *double_ptr, char *line, uint8_t
    group 9 = {M48, M49} enable/disable feed and speed override switches
    group 12 = {G54, G55, G56, G57, G58, G59, G59.1, G59.2, G59.3} coordinate system selection
    group 13 = {G61, G61.1, G64} path control mode
-*/
-
+*/