Some tweaks, added planets, fixed drag

I added some comment tweaks to improve the readability of the drag equations. I also added the rest of the planets/bodies in the game to the script using more exact values from https://docs.google.com/spreadsheet/ccc?key=0AuySrGPsDeq2dFdaS19xc2lobGc2aWNXUkJsZlVtWFE#gid=1
Finally, I fixed your drag equation. You were improperly assuming gamma to be equal to 0.001 which is not the case.