better brakes => block wheels
README: update instructions

update instructions to avoid compiling *~ or *.bak files

Signed-off-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>
work on optimizations
big optimization : only draw blocks and edges that are on the screen zone (with help of aabb from box2D)
optimization : start of double buffer (second canvas)
double buffering optimization : it works but I still have to refresh the buffer canvas and deal with the zoom when I copy the buffer into the main canvas
adaptation of code for buffer of any size
double buffering : the buffer is copied at the right position on the canvas (even with the zoom)
really nice use of double buffering. The buffer redraw automatcally at the moto position when the view of the main canvas go outside of what's in the buffer
double buffer refactoring
Merge branch 'master' into gh-pages