- add option to completely disable
- add iparameter to software manual

With the decision "Adopt to mandate the presence of AU delimiter
for each AU", AUDs are enabled by default and a warning is printed, if
they are disabled. The config parameter should be removed later and the
decoder needs to check for AUD presence.

fix some JCCR related indentation, encapsulation, and descriptive text, add --PYUV to software manual

Fix #426: Chroma QP mapping tables - incorrectly initialized arrays for some encoder configurations.

Software changes with respect to the adoption from proposal JVET-O0455:
Control the maximum number of IBC merge candidates independently from
the maximum number of regular merge candidates.