add a remove function to construction
comment construction.lua
add physics system
move systems into their own directory, add orbital physics sim
add files for love compression
add automatic mode selection
add runge-kutta gravity sim
add scenes directory, using scenes to initialize game world
set background to black
add atmospheric damping
add atmosphere radius
generalize gravity calculation, add interpolator
modify scene2
add fast zoom
set scene1
fix drag for physics, add collision callbacks
add construction to scene constructor
remove explicity mass initialization, use box2d mass