Move static ctor out of unsafe context

[domenukk]

On master, the following test succeeds to mutate and read the mutable static test boolean without the use of an unsafe keyword:

extern crate ctor;
use ctor::*;

static mut test: bool = false;
#[ctor]
static STATIC_CTOR: bool = {
  test = true;
  test
}

This PR fixes the issue

[mmastrac]

@domenukk Thanks for the two excellent PRs. Both are merged and I'll release a new version shortly. If you are interested in contributing more, I'd be happy to add you as a full contributor on the project.

[domenukk]

Thanks for merging! I'll gladly send more PRs if I come across other things :)

[domenukk]

Is there a release on crates with these fixes yet?

[mmastrac]

I just pushed 0.2.5 with a cargo update bump and all the latest changes, so that's definitely up-to-date!

[domenukk]

Thank you! :)