20230309 add openssl feature

[Firstyear]

Fixes #69 - Add support for openssl in this crate.

This is currently a WIP - next I need to clean up the code, improve the acceptor builder, and then write the docs. Putting in the draft now to show the basic elements. Mostly this was modeled on the rustls code, but with the changes needed due to the differences in the OpenSSL tokio bindings.

[Firstyear]

Okay, should be ready for review now. I squashed the commits and did a self review to cleanup comments that were left over and similar. If there is anything you'd like changed, let me know :)

Thanks!

[programatik29]

Seems good. There are few warnings when using cargo clippy --all-features or ideally cargo hack clippy --each-feature. Can you fix them?

[Firstyear]

Done, I resolve all the lints that were added by lines affected in this PR. There are some outstanding though not affected by my change.

warning: this block may be rewritten with the `?` operator
   --> src/server.rs:227:9
    |
227 | /         if let Err(e) = result {
228 | |             return Err(e);
229 | |         }
    | |_________^ help: replace it with: `result?;`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#question_mark
    = note: `#[warn(clippy::question_mark)]` on by default

warning: usage of wildcard import
  --> src/tls_rustls/mod.rs:46:9
   |
46 |     use super::*;
   |         ^^^^^^^^ help: try: `super::{RustlsAcceptor, RustlsConfig, Server, SocketAddr}`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_imports
note: the lint level is defined here
  --> src/lib.rs:88:5
   |
88 |     clippy::wildcard_imports,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^

[Firstyear]

Thank you!