Introduce additional variable axis_homed to replace axix_known_position
when the coordinate display should indicate the axis is not homed.
This is to distinguish between "not homed" and "inexact position possible
because stepper was disabled".

# Conflicts:
#	Marlin/ultralcd_implementation_hitachi_HD44780.h
solved

Implement and test blinking for char-lcds

# Conflicts:
#	Marlin/ultralcd_implementation_hitachi_HD44780.h
solved

Fix crashes when the Z axis is moved via LCD
by calling `plan_buffer_line` only when there is enough room in the
planner buffer, to avoid endless recursion.
A brief description about what went wrong is in #1166

Protect MarlinSerial against interrupts
by shielding the CRITICAL_SECTIONs

Now with a test if RX_BUFFER_SIZE is in the required range.
Code in peek() and read() is now optimized for readability and showing the similarity between the two.

Maybe a bit overprotected in checkRx() and store_char(), but now some days without detected errors from this source.

@thinkyhead
Hi Scott,
your code from a0f362c@thinkyhead is great, but you forgot to skip the
command.
Symptom `M117 Test`shows `M117 Test` on LCD instead of `Test`.

see also
https://github.com/MarlinFirmware/Marlin/commit/a0f362c735
6f8e3c2f17 lines 941, 2851 and so on

Greetings and welcome back

Jochen

* Configuration.h:
  * updated header comment
  * new UUID feature used
  * sync to default config
  * typos fixed
  * changes better documented
  * reflect change in SDSUPPORT feature
* Configuration_adv.h
  * updated header comment
  * thermal protection tuned to work with K8200
  * homing tuned
  * sync to default config
  * typos fixed
  * changes better documented
  * reflect change in LCD features
  * use long filenames
  * use Watchdog
  * use Babystepping
  * use Auto Filament Change

This formalizes the dependency of MANUAL_BED_LEVELING on
MESH_BED_LEVELING

- Include aligned comment about new SDSUPPORT behavior

Development moved to https://github.com/thinkyhead/MarlinConfigurator

The domain is gone and doesn’t redirect, so for now show no URL on the boot screen.

This is a proposed change. This section of M114 output is a debug
extension according to RepRap wiki.

Addresses issue #2715

Send the correct line number.
If no N was in the command - non't send an N.

Replace the "ok" in M280, M301, M304, M851 with output not including an "ok"
to avoid senting two "ok"s for a single g-code.

Doing the same for M105 would break the input filters of the hosts.
For M105 the other "ok" is omitted.

Instead of changing SDEXTRASLOW variable to a slower speed,  the new
SDULTRASLOW is used for rigidbot panel.

Forgot Z2_MIN_PIN