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.

- Nonlinear auto bed leveling code (includes G29, G30, Z_RAISE_AFTER_PROBING). Cleaned it up to be a delta-specific AUTO_BED_LEVELING_GRID code path.
- Allen key z-probe deployment and retraction code. Cleaned it up and added safety checks.

- Moved sanity-checks to Marlin_main.cpp
- Applied to other configuration files
- Fixed formatting of ABL output
- Passing verbose level to probe_pt
- Miscellaneous cleanup
- Put CONFIG_STEPPERS_TOSHIBA into Configuration.h

- A redo of #1576, which missed topo_flag
- Always set verbose_level

add ```^ !(n_ENABLE_ON)``` for each stepper

  * "G1 X1 ; test" was not executing "G1 X1" due to never leaving comment mode.
  * "M117 Hello \;)" printed "Hello \" to the display due to not replacing serial_char properly.

Tested with the following commands:
    * M117 Hello ; test => displays "Hello" on display, ignores "test"
    * G1 X1 ; foo => moves 1mm in X, ignores "foo"
    * ; test => completely ignored, not even acknowledged
    * M117 Hello \;) => displays "Hello ;)" on display
    * M117 Hello \\;) => displays "Hello \" on display, ignores ")"

Autoretract was broken, looks like it was overlooked when the retracted flag was updated for multi extruders.

- Setting boundaries based on configured limits, contrasting with G28
(which forgets these limits?)

- Adapted “Enhanced G29” code referred to in #1499 and posted at
[3dprintboard.com](http://3dprintboard.com/showthread.php?3105-Auto_Bed_
Leveling-Enhanced-G29-command)
- Compatible with current G29 while adding some new arguments
  - `V` sets the verbose level for serial out
  - `T` (or `V` > 2) send a Topology report to serial out
  - `E` works the same way as before
  - `P` works as before (source used `n` or `U`/`u`)
  - `L`, `R`, `B`, `F` work as before
- Still needs sanity checking for `LRBF`