recreated conversion matrices from ITU rec standards
Created originally on Bitbucket by g3gg0 (Georg Hofstetter)
this patch contains the conversion from RGB into YCbCr based on the official ITU rec.
http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-5-200204-I!!PDF-E.pdf
http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-7-201103-I!!PDF-E.pdf
please check if it matches the expectations.