Stack estimation for python 3.8

[joemarshall]

I think the stack estimation code could be updated thanks to a new jump parameter in stack effect in the dis module which now lets you get the stack effect of every instruction in the bytecode including jumps. It's much simpler than how you estimate it and should stay working even if new bytecode turns up.

Check out what I do in https://github.com/joemarshall/unthrow/blob/main/unthrow/unthrow.pyx

(Don't look too hard at the rest of the code though, it is pretty alpha!)

[a-rahimi]

first of all, unthrowing an exception is a clever and inspiring idea. second, thanks for the tip on the new dis functionality. i'll think about how to incorporate it.