an imprecise roadmap of refactoring for 0cc-famitracker

separate ftm save/load methods from cfamitrackerdoc
decouple cinstrument from cfamitrackerdoc
create a bookmark manager class
create a sequence manager class
create a sound chip class (holds cchannelhandler)
decouple cchannelhandler from soundgen
remove delegations from cfamitrackerdoc to cpatterndata where possible
bring back cfamitrackerdocinterface?
decouple cchannelhandler from cfamitrackerdoc

remove chan_id_t except in cchannelhandler ctor