Macro log

macro_rules! log {
    ($name:expr, $severity:expr, $body:expr) => { ... };
    ($name:expr, $severity:expr, $body:expr, $( $attr_key:ident = $attr_value:expr ),+ $(,)?) => { ... };
    ($name:expr, $severity:expr, $body:expr, $( $attr:ident ),+ $(,)?) => { ... };
}