Update Readme descriptions for M200, M207 and M208
Merge pull request #871 from whosawhatsis/fwretract

Update Readme descriptions for M200, M207 and M208
Merge branch 'Marlin_v1' into mendel90_lcd
Update zjerk, recover_feedrate, default_accel, z_home

Signed-off-by: Matthew Schick <matthew.schick@gmail.com>
Merge branch 'mendel90_lcd' into mendel90