Macro event 

macro_rules! event {
    (level: $level:expr, $fmt:expr, $( $key:ident = $value:expr ),+) => { ... };
    (level: $level:expr, $fmt:expr, $($args:expr)*, $( $key:ident = $value:expr ),+) => { ... };
    (level: $level:expr, $fmt:expr) => { ... };
    (level: $level:expr, $fmt:expr, $($args:tt)*) => { ... };
}

Creates a new event in the current span.

The event macro is invoked with a crate::Level, along with a message. The message may be a format string, followed by zero-or-more arguments.