[MMc] Playable Solar Golf

The game is now playable (but not winnable...there is no hole). I left the debug visualizations on because they look neat to a developer. I'm temporarily hosting the game here, try it out!

Debug visualizations while working on coordinate system issues.

Done:                                                                                                                                                        

• generate procedural planet heightfield                                        
• generate physics collision surface
• render stars    
• render planet
• render atmosphere  
• implement arbitrary entities with rigid-body physics                                                       
• gravity for planets  
• implement ball physics
• tune ball physics
• implement dragging out an impulse vector
• draw impulse vector
• mouse impulse     
• clamp maximum impulse
• add subtle gradients to planets to give better intuition for slopes on a curved surface
• add audio feedback for canceled stroke, illegal stroke, and successful stroke
• make the view keep the ball on screen and well-oriented                                                              

Next:

• make the view lead the ball
• place hole
• make hole indicator
• add 2nd planet
• implement rockets
• implement aliens
• place tee