Use pin macro to remove all unsafe

[Manishearth]

[notgull]

Doesn't this raise the MSRV to 1.68.0?

[Manishearth]

oh, I wasn't aware there was an MSRV.

[zesterer]

Ah, yep. MSRV is the current reason for not using pin! (although I'm extremely glad it made it into std!). I believe #16 does the same thing. Perhaps in a few months to a year I'll raise the MSRV but since this crate suddenly seems to be quite popular and sits at the bottom of a lot of dependency trees in the ecosystem, I want to avoid bumping it unless there's a solid, quantifiable reason for bumping. Thanks for opening the PR though :)

[Manishearth]

Sounds good!