docs: Expanded C++ guidelines following suggestions by P. Mackinlay.
ui/inifile.cpp: Got rid of the check for "arcade" systems - it broke
managing favourites for the slotted Neo Geo.
luaengine.cpp: Removed the "type" property from system driver metadata.
It's effectively deprecated.
bus/vme/vme_fcisio.cpp, commodore/mps1230.cpp: Fixed inappropriate use
of machine type flag constants.
megadriv.xml: Made notes about the two Galaxy Force 2 sets more explcit.