Make session public in TlsStream

[xpepermint]

Some very important data provided by Session are currently hidden (e.g. which protocol was selected by the handshake).

Ref: #30

[xpepermint]

@MoMannn when this is merged you'll be able to get the selected ALPN protocol like this:

use rustls::{Session}; // don't forget this
...
connector.connect("google.com", tcp_stream).await?;
socket.session.get_alpn_protocol();

[dizda]

Also waiting for this feature.

[dizda]

I personally need to set some stuff about the session, eg.

session.set_buffer_limit(1_000_000);

[xpepermint]

Status?

[skade]

As stated on other places on this tracker, I don't want to expose rusttls types directly. async-tls is rather intended to implement high-level operations on TLS connections rather than having users implement those themselves. It's also intended to be engine-independent.

I know I'm far away from this goal, as I was sidelined, which is the reason why I put a maintenance notice out, showing a path to a structured handover to new maintainers. It's important to me though that the above design is taken over along with it.