* AEntity.cs, AState.cs, MenuState.cs:
  Initial version.

* Player.cs, BlockSpawner.cs:
  Modified to inherit from AEntity.
  Modified to use GInstance from AEntity instead of the static variable Game.Instance.

* Game.cs:
  Converted to use new state system.

* GameTime.cs:
  Removed trailing lines.

* Program.cs:
  Added help command.