I have not released the source code no. I'm actually developing a full-scale version of this game right now. It's also called Bobls and is on Steam if you are interested.
The slopes in this classic version are extremely simple and basically only works for 45 degree angles. If I remember correctly, I simply do two or three precise collision_point checks to determine if it's an upwards or downwards going slope and move the player directly according to it, or something like that. It's been a while.