- Also patch up some warnings

- Fix a bug reading `code_value` for `M503 Sn`
- Hide and remove unused variables

- Also a small tweak to SanityCheck.h

to avoid:
Marlin_main.cpp:1790: warning: array subscript is above array bounds.

- Init `zprobe_zoffset`
- Remove `current_position[Z_AXIS] = zprobe_zoffset` lines from the
`set_bed_level_equation_*` functions
- Apply standards to `mesh_bed_leveling` files
- Document `MESH_BED_LEVELING`

if not have SDSUPPORT the fromsd array is not necessary

It just probe all the bed without appliying the matrix.
Useful after a first G29 to check the topology.

ZigZag: Inverted Behavior.. If T supplied, it does not zigzag.
Topograph table: The table was rotated 90º clockwise.

Z_DUAL_ENDSTOPS is a feature to enable the use of 2 endstops for both Z
steppers - Let's call them Z stepper and Z2 stepper.
That way the machine is capable to align the bed during home, since both
Z steppers are homed.
There is also an implementation of M666 (software endstops adjustment)
to this feature.
After Z homing, this adjustment is applied to just one of the steppers
in order to align the bed.
One just need to home the Z axis and measure the distance difference
between both Z axis and apply the math: Z adjust = Z - Z2.
If the Z stepper axis is closer to the bed, the measure Z > Z2 (yes, it
is.. think about it) and the Z adjust would be positive.
Play a little bit with small adjustments (0.5mm) and check the
behaviour.
The M119 (endstops report) will start reporting the Z2 Endstop as well.

- Address issue #1669
- Remove the TOPO_ORIGIN configuration setting

- Address #1262 by leaving values as set
- Rename `add_homing` to `home_offset`

- Add `Conditionals.h` with calculated configuration values
- Add `SanityCheck.h` with checks for configuration errors
- Remove equivalent code from all configurations
- Move error checks from some sources to `SanityCheck.h` also
- Fix initialization of count_direction in stepper.cpp

Saves one addition.
Needs one pointer on the stack.

Don't know if this is a go trade.

Shoot in the dark.

Got:
Marlin_main.cpp:2567: warning: unused variable 'codepos'

Needs revision.
Don't now how this should look like.

Got:
Marlin_main.cpp:1689: warning: 'codenum' may be used uninitialized in this function

And indeed codenum is undefined when no parameter is given.

got:
Marlin_main.cpp:387: warning: 'delta' defined but not used

Compiles cleaner when definition is removed.

Users hat to press kill-button for unexpexted lon times.
See #1593

- Addressing issue #1608

- Add support for 4th extruder
- Fix parentheses matching
- Apply coding standards
- Address issue mentioned at #1575

- Add BIT and TEST macros
- Add _APPLY_ macros to stepper.cpp to help with consolidation
- Consolidate code in stepper.cpp using macros
- Apply standards in stepper.cpp
- Use >= 0 instead of > -1 as a better semantic
- Replace DUAL_Y_CARRIAGE with Y_DUAL_STEPPER_DRIVERS

Added option to set Travel Acceleration (non printing moves).
The M204 options was a non sense (S for printing moves and T for retract
moves).

It has been changed to:
P = Printing moves
R = Retract only (no X, Y, Z) moves
T = Travel (non
printing) moves

I will add this info o G-Code wiki in reprap.org. I also advise to put
this info in Marlin next version changelog.

I forgot to enclousure the variable with #ifdef

because strtod() will read the E address value as if it was a base 10
exponent.

With this change a mechanical or optical switch may be used to check the
availability of the filament and when the filament runs out an M600
(filament change) command is issued. This is only done while printing
with an SD card.

This feature was requested several times (issue #679), but the requests
were not accepted since it was believed that this situation should be
handled at host side. However during an SD print the control is totally
on firmware and I think that during an SD print it should be handled by
the firmware.

The original code was posted at reprap forum
(http://forums.reprap.org/read.php?1,297350) by Lazymonk. I have only
corrected some bugs of the code and improved it by adding definitions to
the configuration.h in order to make it more standardized.