ErikZalm/Marlin — pull request #647 by shaggythesheep (2013-11-09 15:14:00+00:00)
Title: Implement M226 - GCode Initiated Pause

Implemented M226 as described here:
http://reprap.org/wiki/G-code#M226:_Gcode_Initiated_Pause

Waits for pin to be become either HIGH, LOW or the inverse of what it
was before. Allows printing to pause until user interaction