Update pins.h

Added DISABLE_MIN_ENDSTOPS
Update Configuration.h

Added DISABLE_MIN_ENDSTOPS
Update pins.h

#ifdef DISABLE_MIN_ENDSTOPS
#define X_MIN_PIN          -1
#define Y_ MIN_PIN          -1
#define Z_ MIN_PIN          -1
#endif
Update pins.h

Added DISABLE_MIN_ENDSTOPS
Merge pull request #2 from Gaweph/master

Min ENDSTOP issue