Fixup last PR

[Jake-Shadle]

• You accidentally merged my previous PR's submodule change, this corrects it to use the 0.3.2 branch of the official repo, sorry about that!
• Fixed use after free bug(s) in Breadcrumb::new(), it would free the strings pointed at by both type and message, which would result in corrupted strings being sent to sentry, and sentry would apparently just completely swallow the event due the corrupted strings and not even report that there was an issue processing the event, oops!
• Reimplemented the crappy workaround I did for adding stacktraces to the exception object on an event so that the stacktrace would show up nicely in sentry. You can use it like this:

let mut eve = Event::new();
eve.insert("level", "fatal");
eve.add_exception(sentry_native::Exception::new("panic", msg), 0);
eve.capture();

Let me know if you like that change and I can document the Exception object (right now it complains about missing docs).