Added blocks and fixed a player velocity issue.

* DebugMenu.cs, Block.cs, BlockSpawner.cs:
  Initial version.

* Player.cs:
  Fixed velocity bug that was based off of the framerate. Changed
  slowing multiplier.

* Game.cs:
  Added regions.
  Added DebugMenu.
  Added generic input handling.

* DifficultyState.cs, ForegroundState.cs:
  Modified to match new state Draw() definition.

* MenuState.cs:
  Modified to match new state Draw() definition.
  Pressing escape while in the menu will now return to the game if a game is in progress.

* State.cs:
  Now inherits Transformable and Drawable.
  New Draw() definition to match Drawable.

* GameState.cs:
  Added BlockSpawner and difficulty handling.
  Modified to match new state Draw() definition.