Add Application class; contains Main()

Ignoring project/* folder, which may contain project files or other
generated files.
Add PhysicsWorld and Vector2D
Add multiple game classes

Object: Base class for everything
Entity: Parent class for anything that exists as part of the game world,
        e.g. creatures, items, the player, etc.
Body: Entity that has a velocity and acceleration, and exists within the
      game's physics world. Classes that inherit Entity but not Body are
      objects that do not move, like buildings or the floor.
Fix missing newlines at EOF
Application: Add Exit() method

Store status variable as a private variable, when Exit() is called, status
gets returned from Run() to the calling function (Main() in our case.)
Merge pull request #3 from palistov/develop

Very nice, thanks!

It would be helpful to keep to the current engine design as it helps everyone keep the same idea of the code structure, without having to read over everyone's code.