[CR] Message explanations for the player's melee misses

When the player misses a melee attack, a weighted list of messages for
melee accuracy penalties is created, and a random one is picked and
messaged. The player will get messages if he has torso encumbrance or is
farsighted and is missing glasses.
Messages for effects that lower dexterity or otherwise indirectly impact
dexterity could be added in the future.

An additional message every miss can get annoying, so I made it happen
with a 1 in 2 chance every miss. This is something that can be tuned.

Closes #6510.