Version 0.6.4

This update took a few days, but it's finally done. The most important change I made was to completely rework the networking code to make better use of the packets it sends. It's also much more stable. It's now much more unlikely that a network connection will be left in an inconsistent state. I'm hoping this will about cut the lag in half.

Other changes:

• Archer spends 3 energy to shoot, up from 2. The fully automatic bow was amusing, but I think this will be more fun.
• I rewrote the manual to make it more concise and friendlier to new players.