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).

- Helper functions for e.g. retrieving and caching UV coords etc. Maybe these
  should be in a separate file?

- objtool: An option to parse material groups and generate an array of 
  per-triangle material indices.

- PC == 2 (and possibly 1) could likely be accelerated by not using interpolate
  functions, but rather FastLerStates for the values recomputed after each
  row segment.                                             DONE (doesn't work
                                                                 for PC == 2,
                                                                 tried)
- 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

- function to map one point in 3D space to screen, along with size (for mapping
  billboards/sprites etc.)                                 DONE

- Optimize persp. correction!

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

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

- 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:

repeated:

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