Fixing cl_mul

Hey,

I managed to get the test under `examples/broken/` to compile and run without errors. I'd love to see that work shared with the community.

BTW awesome job on this project!

I see that you use lists:map/2 a lot in your code; have you thought about using list comprehensions instead? They are said to be generally faster and I believe more readable. Also there are a lot of tabs and trailing spaces in your code. Do you mind merging them if I work on those things?