Macro log 

macro_rules! log {
    ($log_level:expr, $($format_string:literal)PW_FMT_CONCAT+ $(, $args:expr)* $(,)?) => { ... };
    ($log_level:expr, $format_string:literal $(, $args:expr)* $(,)?) => { ... };
}

Emit a log message using core::fmt format string semantics.

log takes a LogLevel, a core::fmt style format string, and necessary arguments to that string and emits a log message to the logging backend.

use pw_log::{log, LogLevel};

log!(LogLevel::Info, "Log fact: A {} log has a Janka hardness of {} lbf.",
     "Spruce Pine" as &str, 700 as i32);

Multiple string literals can be concatenated using the PW_FMT_CONCAT operator.

This is particularly useful when writing wrapper macros that need to prepend a prefix to a format string.

use pw_log::{log, LogLevel};

macro_rules! my_info_log {
    ($format_string:literal $(, $args:expr)* $(,)?) => {
        log!(LogLevel::Info, "[MyModule] " PW_FMT_CONCAT $format_string $(, $args)*)
    };
}

my_info_log!("The answer is {}.", 42 as i32);