That concept was added more for completeness than for actual usefulness,
since I have not used it a single time since its creation. Given the
complexity of the library, I think it is better to remove it and shrink
the library to a more useful core than giving too many features that
contribute to bloat.
Also, the laws were difficult to check and it hence Traversable models
were not very well tested anyway.
I can always roll this back if someone shows me how Traversable is
actually useful for metaprogramming.
