Function slog_envlogger::init

pub fn init() -> Result<GlobalLoggerGuard, SetLoggerError>

Use a default EnvLogger as global logging drain

This is for lazy devs that with minimal amount of work want to convert software that used standard Rust env_logger crate to slog-env_logger.

It's an easy first step, but using init() you're not gaining almost anything that slog has to offer, so I highly encourage to use new() instead and explicitly configure your loggers.