scroll-1.20151219: TODO

For spells with only 1 component, add a letter frequency table, and make
the charmap be constructed by picking a letter with the desired frequency
that is not otherwise used. This adds a different sort of randomness to the
game.

I've had 2 reports of it crashing after winning the game, with:

scroll: ./Data/Vector/Generic/Mutable.hs:590 (read): index out of bounds (6,6)

The typescript fileG0A3Np on clam should show this happening.
as should filecobD95 and fileOlHEMR on elephant.

"Game exploded when I maximized the terminal window." -- tmp/fileBQE03e

"I think I went into a dream while stunned, and came out permenantly
stunned." -- tmp/filehgwH0C on clam

Casting a spell should only use 1 of each spell component even when
multiple are swallowed. This would allow stacking spells (eg, "new new x")