Create documentation for the algorithm

[simondemeule]

The main interest of this project are the improvements made to the classical curved path integration algorithm. While these are somewhat explained in the code comments, they are hard to understand without a good understanding of the program structure. They should be made clearer by defining them using pseudo-code, and by talking about them in a more mathematical, implementation-independent way. Having a few sketches to show the spatial intuition behind the algorithm would be great. Maybe this can take the form of a small paper, or a blog post.