fruits are now forcibly aligned in nice columns. Vertical matches and falling work beautifully now, but fruits no longer match horizontally. That'll be fixed in the next commit, before this one is pushed to github. #8 #2
Rewrote match detection to use a grid. Fixes #8, fixes #2.

The physics system is still the authoritative source for where blocks are. Matching takes their xy-positions and crams them into a grid, built every time we try to match something.

This probably runs a little slower. I'm not seeing any noticeable difference, but phones might not like rebuilding the grid every time. Haven't tested it though, and phones will likely use far fewer blocks anyway, so let's worry about that later.