Macro pw_log::warnf

macro_rules! warnf {
    ($($args:expr),*) => { ... };
}

Emit a warn level log message using printf format string semantics.

use pw_log::warnf;

warnf!(
    "Log Fact: Made from a log, an %d year old dugout canoe is the oldest discovered boat in %s.",
    8000, "Africa");