Removed 2 hardcoded values.
Changed algorithm in src/bag.c to be more efficient.

Relatively small change to the algorithm in src/bag.c.

The problem is to put the blocks into the bag randomly.

Before, we picked a random number and checked if it was available and if it was
we added it to the bag, then marked it dirty. Then we guessed again, etc. This
was very inefficient and wasted lots of cycles.

Now, we pick a random number up to the number of pieces remaining, and use that
number to select that element in the list of available pieces.

Example: If the bag contained 3 pieces: T, O, S, we would choose a number
between [1, 3] and then search through the list of remaining blocks to find the
third element.

Also I drew an ASCII diagram. I think it looks atrocious.
Fixed some whitespace. And rewrote a comment for accuracy.
added declaration for ghost_block
rearranged some functions to their logical groups
generate random bag during game init
added ghost block init code
Changed Pause and Quit keys to P and O.

Game doesn't count down pause ticks when building in debugging mode.
Removed vestigial debug output.
Prevent user from moving pieces when paused.
Added 'G' key to toggle drawing the ghost blocks.
Accidentally removed variable in white-space formatting.
Tell user when they're using a debugging build.
Use user's USER environment variable as username by default.

Whitespace changes.
Draw Next/Hold blocks verticle and in their own box.

This commit is ugly; I should have commited somewhere inbetween these two
logical changes.

The first moves the Next/Hold block lists to a verticle position and draws a
box around it, maybe some other stuff.

The second actually changes how we draw. I was getting an extremely annoying
flash as the screen would update. So now we don't redraw the block lists unless
they've changed. We also try not to use wrefresh() inplace to
wnoutrefresh()/doupdate(). Which should help the throughput. Finally, we don't
draw anything if the game is paused.
Version bump to .25
Fix whitespace. Redraw pause ticks even when paused.