RUSTSEC-2018-0020

Affected versions contained a possible use-after-free issue with property list iteration due to a lack of a lifetime constraint tying the lifetime of a `proplist::Iterator` to the `Proplist` object for which it was created. This made it possible for users, without experiencing a compiler error/warning, to destroy the `Proplist` object before the iterator, thus destroying the underlying C object the iterator works upon, before the iterator may be finished with it.

This impacts all versions of the crate before `2.5.0` back to `1.0.5`. Before version `1.0.5` the function that produces the iterator was broken to the point of being useless.