Made the double touch portion a conditional compile based on the
PROBE_DOUBLE_TOUCH flag.
==============================================
Bugfix
The current G38 only stopped a move if it involved the Z axis.
Moved all the G38 code to it's own section and put it where it would
always be executed no matter what axis was moving or if the endstop was
enabled.
Also added a comment to configuration_adv to alert the user the double
tap had to be turned on.
==============================================
Change G38 back to using Z_MIN_PROBE
There's no Z_MIN endstop if Z_DUAL_ENDSTOPS is enabled and you have them
set to the top of the gantry.
G38 started out as using the Z_MIN_PROBE pin. I don't remember why we
changed it to the Z_MIN endstop.
The target here is to update the screens of graphical and char base
displays as fast as possible, without draining the planner buffer too much.
For that measure the time it takes to draw and transfer one
(partial) screen to the display. Build a max. value from that.
Because ther can be large differences, depending on how much the display
updates are interrupted, the max value is decreased by one ms/s. This way
it can shrink again.
On the other side we keep track on how much time it takes to empty the
planner buffer.
Now we draw the next (partial) display update only then, when we do not
drain the planner buffer to much. We draw only when the time in the
buffer is two times larger than a update takes, or the buffer is empty anyway.
When we have begun to draw a screen we do not wait until the next 100ms
time slot comes. We draw the next partial screen as fast as possible, but
give the system a chance to refill the buffers a bit.
When we see, during drawing a screen, the screen contend has changed,
we stop the current draw and begin to draw the new content from the top.
lcd_update can take so much time that the block buffer gets drained if
there are only short segments. This leads to jerky printer movements for
example in circles and a bad print quality.
This change implements a simple check: Only if the block currently
executed is long enough, run lcd_update.
This also means the printer will not show actual values on the LCD nor
will it respond to buttons pressed. A option that keeps the menu
accessible is also available.
Aditionaly, slow down if a block would be so fast that adding a new
block to the buffer would take more time. In this case, the buffer would
drain until it's empty in worst case.
