GlRenderer: Fix background color

* It should be (.1, .2, .3) instead of black.
test43_object.cpp: Remove unnecessary include

- No, I have nothing else to do
GameObject::Data: Add backlink to object

+ It makes sense to have a link to the GameObject it belongs to in every
  GameObject::Data object
FlappyBox: Logic and Drawing

+ Add FlappyBox logic, engine and model
+ Add draw view
.gitignore: Ignore cscope files

+ I have them, you don't need them
FlappyBox: Playing (4.4 done)

+ Add sound view
BoxObjectLogic: Limit angle

! Limit angle to [0, 360) in order to avoid overflows
BoxObjectLogic: Fix exponential decrease

! The decrease should depend on the last time step
Merge pull request #1 from roidanton/abcdefghijklmnopqrstvwxyz

Pull abcdefghijklmnopqrstvwxyz