Improve SimplePlayer

[cangiuli]

Although I would like to SimplePlayer to remain fairly straightforward, there is clearly much room for improvement:

• Keep track of extra information implied by save clues, and act on it
• Can discard clued cards when they're guaranteed to be useless (discardOldestUnclued)
• A card is also useless when unreachable (isUseless)
• Several 5's usually end up in the discard right now

We can also collect ideas for a more complicated player:

• Finesses
• Reverse finesses
• Bluffs
• Awareness of the endgame