Re-export ffi crate and foreign-types traits

[dhouck]

Closes #2020

I also re-exported the ffi crate, for the same reason; I can remove that part if it isnʼt wanted, but it seems reasonable to me for the same reason I mention there.

At a quick glance I couldnʼt find other things that obviously looked like they should be re-exported.

[dhouck]

I just confirmed that this PR does not touch the file Clippy is complaining about, or indeed anything in openssl-sys. I do not know why this PR fails that check when my previous PR passed it and the relevant files have not been changed since that previous PR was made.

The rustfmt check is entirely on me, though; fixing that now.

[dhouck]

I cannot figure out why clippy started complaining now. GitHub updated the test runner images, but the new one has the same version of all rust tools and of the openssl libraries. I can see the issue itʼs complaining about has existed for two years. I cannot get Clippy to complain on my machine, although that might just be that I should have been in bed hours ago.

In the morning, Iʼll make another PR to fix the problem Clippy is complaining about, then hopefully once thatʼs merged I can rebase this one and itʼll pass all checks. But it still bugs me that something changed and I have no clue what.

[romen]

@sfackler what is the status of this PR? Are there plans to merge it in the foreseeable future or is something holding it back?