bullet counter

Closes #24
display fps
smaller font
Don't change msg every frame
zoom a bit
use Arg
Limit FPS (kind of)

Closes #26
Merge branch 'sdlperf'

* sdlperf:
  Limit FPS (kind of)
  use Arg
  zoom a bit
  Don't change msg every frame
  smaller font
  display fps
  bullet counter