Added M112
Added estop handling
Test and refactor
Merge pull request #851 from DanNixon/estop

Implemented M112
Add M112 description to Marlin_main
Added thremistor table for black thermistor from RepRap-India.com
Signed-off-by: aSensar <admin@asensar.com>
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1