Add py-simplegeneric 0.8.1

The simplegeneric module lets you define simple single-dispatch generic
functions, akin to Python's built-in generic functions like len(), iter()
and so on. However, instead of using specially-named methods,these
generic functions use simple lookup tables, akin to those used by e.g.
pickle.dump() and other generic functions found in
the Python standard library

(markd)