features:

- presets that can be optionally selected and  will configure other constants
  (e.g. a "low memory sort strategy" will turn z-buffer off and turn
  back-to-front sorting on).

- function for computing normals and lighting

- triangle sorting:
  - back-to-front (slower, better memory efficiency)       DONE
  - front-to-back (faster, but needs 1bit stencil buffer)  DONE

- function to set/clear stencil buffer -- can be useful

- Optimize persp. correction!

- Create and use the same function for determining CW/CCW AND left/right vertex
  determination in triangle drawing.

- Check (and possibly fix) if any barycentric coord ever exceeds the range
  <0,255> due to rounding errors etc.

- dithered barycentric interpolation function that is faster than normal
  interpolation -- it will randomly picky one of three values, with greater
  probabilities at greater coords

- option to disable baycentric coordinates computing    DONE

- Z-buffer:
  - full                                  DONE
  - reduced (resolution and precision)    DONE
  - more reduced (4-bit)

- MipMapping? Add triangle size to pixelInfo.  DONE

- perspective correction modes:
  - none                                    DONE
  - full                                    DONE
  - approximate                             DONE

- predefined 3D shapes:
  - cube                                    DONE
  - sphere
  - cylinder
  - pyramid
  - plane

- Depth computation during rasterization -- this should be an optional thing,
  specified with a define (S3L_COMPUTE_DEPTH), which may be turned on
  automatically for some modes (e.g. Z-buffer). It should be computed by the
  fast lerp and passed in the PixelInfo struct.    DONE

- Python tool to convert obj to C array            DONE

- Python tool to convert texture images to C array DONE

- create demos:
  - model viewer                                   DONE 
  - game-like demo (GTA-style, Quake style etc.)
  - offline HQ (lerp texuring, normal mapping, reflections, ...) rendering
    to PPM image file

- drawModel: create an option that would use a cache to not transform the same
  point twice

- Optional rendering stats (FPS, rendered triangles, ...).

- profiling functions for optimization

bugs:

- Determining CW/CCW for a triangle is not 100% exact, sometimes leaves holes
  in models (some very thin triangles)!

- Barycentric coodinates can get wrong in these ways:
  - Any of them can exceed the range <0,511>
  - b0 + b1 can be > 511, which causes b2 (= 511 - b0 - b1) to be negative!

repeated:

- valgrind (and similar) checks
- optimize
- write tests/benchmarks