Macro diag_log

macro_rules! diag_log {
    ($logger:ty { $severity:expr, $verbosity:expr } => $msg:literal) => { ... };
    ($logger:ty { $severity:expr, $verbosity:expr } => $msg:expr) => { ... };
    ($logger:ty { $severity:expr, $verbosity:expr } => $fmt:literal, $( $params:expr ),*) => { ... };
}