Not sure if I should add a RwLock for the ptrace state too...

It's happening...

WIP mainly because we *should* use thread locals, but #[thread_local]
causes segfaults.

This was just my attempt at being smart, I didn't realize
`compare_exchange` returned the old value (I'm dumb!), so I thought
that if the value was 1 then it must have become 2. Normally with
small errors like these you should leave a comment explaining why, but
really, compare and *exchange* is pretty obvious. My bad.

See #151