Added blacklist files.
The application black list is now handled by SystemCollection.
SystemCollection: Used the break keyword instead of continue...
Game is now an interface, System is only a game detector.
MegaDiiveGame: set the version to the local country.
MegaDrive: removed all RomData references.
Library: replaced add_game(system, uri) by add(game).
SystemCollection: replaced game_found(system, uri) by game_found(game).
GameData: lots of changes.
GameData: added Version and Cover objects.
Use a Range for player number.
REDME: Added to-do and contact sections.
Remove un-needed prints.
Add library usage doc(test) in README
Effectively use db_dir in Library's constructor
Remove dead doctests
Moved RomData to its own namespace.
GameData.Game: fixed the missinh initialisation of world in the constuctor.
Added Mega Drive cartridge icons.
Added an entry to the to-to list