PyObject::extract::<Vec<i32>>() cannot be called

[dgrunwald]

src/objects/list.rs:252:37: 252:58 error: the requirement `for<'s>  : 's` is not satisfied (`expected bound lifetime parameter 's, found concrete lifetime`) [E0279]
src/objects/list.rs:252         let v2 = list.into_object().extract::<Vec<i32>>().unwrap();

I've looked into this issue, but I don't think it can be solved at the moment -- in the end, all my attempts run into the problem that I need either 'source : 'prepared, and such a constraint is incompatible with the use of the HRTB on PyObject::extract.

I've even tried to get rid of the 'source lifetime on ExtractPyObject (see extract_vec branch); but that only moved the problem to the 'python : 'prepared constraint.

Maybe the problem will finally be solvable if I also get rid of the 'python lifetime (#15).

[dgrunwald]

Removing both 'source and 'python solved the problem.