Macro trace_dbg

macro_rules! trace_dbg {
    (target: $target:expr, level: $level:expr, $ex:expr) => { ... };
    (level: $level:expr, $ex:expr) => { ... };
    (target: $target:expr, $ex:expr) => { ... };
    ($ex:expr) => { ... };
}

Alias of dbg! for avoiding conflicts with the std::dbg! macro.