ROTATION
--------
STEP 1:
Drop the rotate() functions and make a datastructure which holds all the
shapes (and their rotated versions).

typedef struct
{
  int x,y;
} block_t;

typedef struct
{
  int color;
  int next;
  block_t block[NUMSHAPES];
} shape_t;

We then just hold the current blocknumber, when we rotate it, we replace it
with it's the next field, and so on.

STEP 2:
Also, make the board a one-dimensional array and get rid of the block_t
structure. The shape_t structure should look like this then:

typedef struct
{
  int next;
  int block[NUMSHAPES];
} shape_t;

Just make a array with the initial 7 colors, and keep that color until the
next piece is chosen. This should prove to be the optimal solution.

SCORE
-----

Ok, here's what I could figure out and what I think should be used.

1. We count the number of lines that a piece drops when the user press SPACE,
2. Add 1 to that when we figure out that the block has come to rest,
3. Multiply above by the current level,
4. If "Show Next" is enabled, divide by two, else take as is, and add the
   result to the score.

Of course, we should add 2 instead of 1 to prevent loss of precision in step
4, and the displayed score is then the score / 2.

TIMING
------

Here's what I'm going to use:

1. There is 9 levels, numbered from 1 to 9. We allow 1/level of a second to
   pass before we drop each block one line.

2. After each ten lines that is removed, we increase the level automatically,
   unless the player is already at the highest level (level 9). CAVEAT: If the
   user starts at a higher level than one, we pretend he didn't when we come
   to increasing levels, e.g. if he/she started at level 3, 30 lines must be
   dropped before we go to level 4.

3. I still have to decide whether to use the BSD type delaying (the type I'm
   currently using) or to do it the way I first did it (the signal handler
   method). The question remains which one is the most playable and which
   one is the most portable.