Update dependencies (mostly `rustls`)

[dnaka91]

Update all dependencies to the latest version, especially breaking versions of rustls and related machinery.

Note: This builds on top of #14 as the project doesn't build without it. Therefore, I'll rebase this PR after the merge or the repo is fixed by other means.

Note 2: We might not want to depend on ring directly and let the user of the crate choose which crypto provider to use.