Make logging optional

[anna-is-cute]

Reference to rustls/rustls#22.

Having log be an optional crate is great in rustls. However, this crate depends on rustls with no way to turn off logging, which really, really looks bad in binary crates (especially since rustls prints out all of this debug info in the INFO log level instead of DEBUG).

Please either make logging an option here or turn it off.

[lucab]

However, as logging is a default feature of rustls, in order to turn it off you'll need to go after every single dependency of your project and convince them to opt-out or expose a feature. I don't think this will scale out well. Some alternatives could be:

• use slog to disable chatty levels at compile time
• make logging a non-default feature in rustls (i.e. opt-in)
• adjust log max_levels

[anna-is-cute]

Making logging non-default in rustls would be good, as this is generally what's expected of that kind of library, and I'm surprised this isn't already the case.

Having rustls = { version = "whatever", no-default-features = true } is still possible in this crate, as well. Can definitely have a feature that enables it or disables it, as well.

[g2p]

Fixed in #156