Updates!

c2048.[ch]:
- now use uint32_t instead of uint16_t for board cells.
- now with more comments... sort of

c2048_ai.[ch]:
- we now have the weights for the AI in the structure to make them
  easier to adjust.
- c2048_ai_find_moves now tracks to see if a move has been found
  instead of just returning -10000.f if no move is found.
  No move found is now worth 0.0f, there is a new weight that can be
  adjusted to allow the AI to consider how bad finding no moves is.

main.c:
- Adjusted weights smooth_weight, mono2_weight to 0.0f... game runs
  better without it. These components are from Ov3y's AI.
- Changed how AI_DO_MOVES & AI_LOOK_MOVES actually work in logic, no
  longer hit the zero move bug.

tinyrand.h:
- Comments.