Macro log_once

macro_rules! log_once {
    (@CREATE STATIC) => { ... };
    (target: $target:expr, $lvl:expr, $($arg:tt)+) => { ... };
    ($lvl:expr, $($arg:tt)+) => { ... };
}

Standard logging macro, logging events once for each arguments.

The log event will only be emitted once for each combinaison of target/arguments.

This macro will generically log with the specified Level and format! based argument list.

The max_level_* features can be used to statically disable logging at various levels.