Refactor|libcommon: Standardize G_Map*() argument interpretation wrt current map
Refactor|libcommon: Switched hu_lib.c to C++
Refactor|libdoom64: Switched d_refresh.c to C++
Refactor|libdoom: Switched st_stuff.c to C++
Refactor|libhexen: Switched hrefresh.c to C++
Refactor|libdoom|libdoom64|libheretic|libhexen: Intermission APIs for all games are now C++ only
libdoom|libdoom64|libheretic|libhexen: Cleanup intermission for all games
libdoom|libdoom64|libheretic: Clarified wbstartstruct_t usage, made const
Refactor|libdoom|libdoom64|libheretic: Intermission now uses URI to reference maps
libcommon: Parse map references in map cycle rules into URIs

Todo for later: We should allow using URIs in such rules.
Fixed|Client: Build error (writing de::String through fprintf)