Exogene updated

I released an update to Exogene today. This update significantly adds to the playability and fixes some lingering issue with the underlying serge engine.

I added four new levels. These are actually four of the most fun levels I think. In addition, I added a "reverse" mode where you can play the other levels in reverse mode - ie the enemies move from the red to the green areas. It is nice to play the levels in reverse as it makes a nice change of pace. Some of the levels are not quite balanced correctly in this mode but that is no bad thing either.

In addition I fixed a lingering issue with serge when pymunk was not present. The simplevecs implementation of Vec2d was a bit hokey and could cause some annoying effects in the game. I was able to replace this with the pymunk implementation without adding a dependency. I'll see how this works out but it looks good initially.