Macro trace 

macro_rules! trace {
    ($($arg:tt)+) => { ... };
}

Logs at Level::Trace: every step, for when nothing else has worked.

Shares a name with crate::trace, the profiler module, which is legal — they are in different namespaces — but means a doc link to either has to say which: [mod@trace] for the module, [trace!] for this. use crcbl_core::trace; imports the module and leaves this reachable as crcbl_core::trace!.

crcbl_core::trace!("pumped {} events", 3);