added acceleration and player stops on hitting obstacle

The increased starting speed was a bit abrupt so I added acceleration, I think it takes about 5 seconds to get up to full initial speed

The player also stops dead on hitting an obstacles and accelerates back to their current speed, I'm not sure that is good for the game because it turns into a series of starts and stops as your top speed gets faster

I don't think its quite possible to "go infinite" but you can get a pretty high score depending on your spawn luck

there is already a scaling mechanism for scoring but I think I'll add it to spawning as well so less targets spawn the slower you are going or they take longer to spawn