Add openssl and rustls features

[dodomorandi]

This could be the first step toward improving the situation around #83: if we can remove dynamic libraries, it is much easier to cross compile. Obviously, openssl feature is by default to avoid breaking changes.

Unfortunately, this is not enough to cross-compile against armv6l, it looks like ring is not happy.

This is blocked by Morganamilo/aur-depends#4

[Morganamilo]

#83 is blocked by cargo erroring out weirdly on 32 bit arches. paru links to alpm which in turn links to openssl so I don't see any point in this being a feature.

[dodomorandi]

I understand, and if you think that this is not worth, close the PR without worries. I noticed that you were already supporting both openssl and rustls in your dependencies, I thought that it could be a very tiny helpful step.

[Morganamilo]

Yeah it's in raur cause it makes a bit of sense because you're not locked into openssl via alpm.