Speed up QUICK_HOME feedrate for diagonal move

Speed up the diagonal move while still keeping each individual axis at
or below its homing feedrate.
Merge pull request #888 from whosawhatsis/quick_home

Speed up QUICK_HOME feedrate for diagonal move
Merge branch 'Marlin_v1' into Schultzes
Update Configuration_adv.h

Corrected error in AUTOTEMP instructions
Update Marlin_main.cpp

Added description of autotemp flags to M109
Merge pull request #893 from MyMakibox/patch-1

Update Configuration_adv.h
Merge pull request #894 from MyMakibox/Marlin_v1

Update Marlin_main.cpp
Merge branch 'Marlin_v1' into Schultzes