Three packing methods

Hi all,

I have implemented three methods for packing the watermelons: checkerboard, compact, and rings around the trees. Please see them in src/watermelon/group6/Player.java. Currently the player just chooses the packing methods that generates the largest score, and returns the corresponding seed list.

I also found some problem with the simulator. It didn't have correct values of distoseed, distowall, and distotree. I just sent the patch to Bingyi, and my modified version has also been pushed to github. Let me know if there's any problem.

Thanks,

Wangda