Added a feature to have filament change by gcode or display trigger.
[default off for now]
syntax: M600  X[pos] Y[pos] Z[relative lift] E[initial retract] L[later retract distance for removal]

if enabled, after a M600, the printer will retract by E, lift by Z, move to XY, retract even more filament.
Oh, and it will display "remove filament" and beep like crazy.

You are then supposed to insert a new filament (other color, e.g.) and click the display to continue.
After having the nozzle cleaned manually, aided by the disabled e-steppers.
After clicking, the printer will then go back the whole shebang, and continue printing with a fancy new color.
Chenged LED_PIN for Melzi boards, added comment about broken versions of the Sanguino libraries
Fixed typo in comment
compile fix: quickStop() needs stepper.h
Extended comment explaining M42 usage
Also skip .files and _files with long filenames
Revert "Extended comment explaining M42 usage"

This reverts commit 01541ee64ca1239c9bfa593c54085ae78e0b78ec.
Added comment about M42 usage (clean)
Merge pull request #374 from kintel/quickstop

compile fix: quickStop() needs stepper.h
Merge pull request #371 from Banjer/Melzi_LED_PIN

Chenged LED_PIN for Melzi boards, added comment about broken versions of...
Merge pull request #376 from kintel/skip_longfilenames

Also skip .files and _files with long filenames. I think its better than before. If somebody dislikes it, or wants additional configuration, it can be done in a future step. Thanks, Marius, and nice to have you helping!