Introducing YCG3/YCG4 compression + fixes

- YCG3 is YCoCg with Gamma 2.0 colorspace, giving more precision at low
color values (-ycg3 switch).
- YCG4 is YCoCg Scaled Gamma 2.0 (-ycg4 switch).
- Commandline parms now scanned after options file is loaded. This makes
commandline parms effectively override options, hich is expected
behavior.
- "-ap" commandline parm now work for compression to folders" too. So it
is spelled as "add path" now.
- Fix bugs on decompressing YCG/YCG2 files.