Function scope 

pub fn scope<SF, R>(logger: &Logger, f: SF) -> R
where
    SF: FnOnce() -> R,

Execute code in a logging scope

Logging scopes allow using a slog::Logger without explicitly passing it in the code.

At any time current active Logger for a given thread can be retrived with logger() call.

Logging scopes can be nested and are panic safe.

logger is the Logger to use during the duration of f. with_current_logger can be used to build it as a child of currently active logger.

f is a code to be executed in the logging scope.

Note: Thread scopes are thread-local. Each newly spawned thread starts with a global logger, as a current logger.