Respect `RUST_LOG` environment variable

[orhun]

Is this possible to change the default logging level based on the value of RUST_LOG environment variable? I tried setting it but it had no effect.

[gin66]

RUST_LOG is not supported by tui_logger and IMHO only used by env_logger.

Nevertheless, the application could extract the info from RUST_LOG and initialize tui_logger with several calls of tui_logger::set_level_for_target(). If there is a good PR with opt-in possibility (e.g. feature), then tui_logger can be extended accordingly.

[orhun]

Got it. I did the following for now:

    tui_logger::init_logger(if let Ok(log_level) = std::env::var("RUST_LOG") {
        LevelFilter::from_str(&log_level)?
    } else {
        LevelFilter::Trace
    })?;

You are right about the env_logger part. I started to implement this feature for tui-logger and after some point I realized I was writing identical code to env_logger. So it seems like it is best to keep this feature separate for now.

BTW are you thinking of releasing a new version soon? I'm waiting for #33 and #34 to use them in my application 🐻