minor: fix indentation

ocp kicking in
surface: adds sdl-load-bmp
refac wip: moves foreign types decls to separate file

two problems with defining the types in the file they 'belong' to.

1. circular dependencies
  example: sdl-render-copy.

  should really be defined in renderer.scm but needs SDL_Texture to be
  defined, which by the old convention would be in texture.scm but needs
  SDL_Renderer to be defined.

2. extension libraries
  sdl2-img bindings (coming soon) need acces to the definition of
  SDL_Texture and SDL_Renderer (for now) at compile time. Need to either
  redeclare them there or include the file defining them directly. This
  is very mucn a hack, the same hack applied in the sdl-base egg.
texture: adds rudimentary support

for now includes all available flags and access modifiers as well as
basic functions for creating, destroying and querying textures.

the querying code leaves a lot to be desired. for now we need one call
for each texture parameter you're interested in.